The show's four main characters appeared in all 234 episodes of the show, and, in the opening sequence, were introduced in the following order:
The Cleavers-from left: Hugh Beaumont (Ward), Tony Dow (Wally), Barbara Billingsley (June), Jerry Mathers (Theodore AKA "Beaver").
June Evelyn Bronson Cleaver (Barbara Billingsley) is the wife of Ward Cleaver and the mother of two sons, Wally and Beaver, who is also the main character of the series. She grew up in the Mayfield area and summered with her aunt, Martha Bronson, at Riverside, a community a few hours from Mayfield. June attended boarding school, dated Ward in her teens, and attended college. June mentions that her Aunt Martha "practically raised her". When Beaver asks her about her life, June doesn't mention she ever held down a full-time job. She merely indicates she had a part-time job and was dismissed when she got her books messed up so bad. When the show opens, she is a full-time wife and mother, often seen tidying the house, preparing meals in the kitchen, or tending her family. Her outside interests include social events such as weddings and her sons' school events. In the later seasons, many episodes feature a brief "after-school" scene in the kitchen for June and Wally. Wally breezes through the back door and regales his mother with a short recital couched in teen-speak of his school day. The camera zooms-in on June's amusingly mystified countenance as Wally trots away with a hot dog or other snack-in-hand. During the course of the series' run, June has several housekeepers, including Minerva, Mrs. Manners (who smells like gingerbread according to Beaver), Mrs. Manners' teen daughter Margie (who becomes a romantic interest for Wally), and other unnamed women. Actress Barbara Billingsley appeared in the pilot, every episode of the series, and in the show's spin-offs. Throughout the series' run, she wore either a necklace or a dress with a high collar, jabot, or scarf to hide a surgery-inflicted hollow in her neck which would have caused on-screen shadows.
Ward Cleaver (Hugh Beaumont) is June's husband, and the father of Wally and Beaver. He is a farmer's son who grew up on a farm near Shaker Heights, a community in the vicinity of Mayfield. It's never stated Ward went to the same prep school as June but it is established he dated June in high school, and majored in Philosophy at college. He was an engineer in the Seabees during World War II and, through the show's run, works in a white collar office job, though the nature of his work is never specified. A co-worker, Fred Rutherford, is also a friend and the two men socialize outside the workplace. Though Ward speaks of his father and siblings when recalling his childhood, only his globe-trotting uncle Billy pays visits to the Cleaver home. Ward drives a Plymouth throughout most of the series usually a top line 4 door sedan. and plays golf at a country club. Ward and his wife sleep in twin beds and have a portable television set in their bedroom – the only TV in the house until the last few seasons at which time a console TV (rarely used) stands in Ward's first-floor den. In one episode, Beaver allows a tramp to bathe in his parents' bathroom. The tramp then absconds from the Cleaver house wearing one of Ward's suits and a pair of his shoes. Ward is a good-natured, understanding man who is often called upon to give his sons some moral instruction regarding their choices and behavior. Actor Hugh Beaumont often played villains and heavies in film and television before capturing his signature role as Ward Cleaver. Just before beginning filming a new season for Leave It to Beaver, Beaumont flew from his home in Minnesota to Hollywood while his wife, son, and mother-in-law drove. An accident on the road killed his mother-in-law and severely injured his son. Jerry Mathers later stated that Beaumont's entire participation in the production was seriously impaired by the tragic accident, with Beaumont often walking through his part. Beaumont wrote the story for one episode from the second season, "A Horse Named Nick", and directed a number of episodes in the last two seasons, including the final, retrospective "Family Scrapbook". The character of Ward was portrayed by Max Showalter (credited as Casey Adams) in the pilot episode, "It's a Small World".
Wally Cleaver (Tony Dow) is the son of Ward and June Cleaver and the older brother of Beaver. When the show opens, Wally is 12 and in the eighth grade at Grant Ave. Grammar School. He is an above average student and a top-notch athlete, eventually lettering in three sports. Wally is popular with his peers as well as adults, and, has little difficulty attracting girlfriends, among them Mary Ellen Rogers and Julie Foster. The girls referred to Wally as "the absolute most." His pals include Tooey Brown, Chester Anderson, the awkward Clarence "Lumpy" Rutherford and smart-aleck Eddie Haskell. Wally comes down hard on both Lumpy and Eddie when they pick on Beaver. Wally acts as a bridge in the show between his parents and his brother, often translating parental communications into kidspeak for Beaver's benefit and keeping Ward and June informed of Beaver's feelings, plans, and whereabouts. Leave It to Beaver was actor Tony Dow's first dramatic experience. He would later play the role in spin-offs. The character Wally was portrayed by Paul Sullivan in the pilot episode.
Theodore "Beaver" Cleaver (Jerry Mathers) is the younger son of Ward and June Cleaver and Wally's brother. When the show opens, Beaver is seven years old ("almost eight") and in the second grade at Grant Ave. Grammar School. Beaver is all-boy with baseball, carnivals, comic books, money-making schemes, and animals of all kinds high on his list of interests while very proper ladies, dance lessons, bathing, and homework test his patience to the limit. Through the series' entire six-season run, Beaver shares a bedroom and adjoining bath with Wally. In one episode, he moves into the guest room after a spat with Wally but returns to the safety of his old bedroom when shadows in the guest room spook him. Beaver is not the athlete his brother is, but he does play football and wins his school team's Most Inspirational Player award. He also performs in many school plays. Beaver has several one-shot pets (an alligator, a rabbit, pigeons, and other creatures) through the series' run. Though Beaver has many friends his own age, his best friend is Gus, an old fireman in the neighborhood, who gives Beaver sound advice and tries to keep the boy on the straight and narrow. Beaver wants and tries to do the right thing but cannot help going astray and usually faces a moral lecture from his father at the end of each episode regarding some misadventure he has suffered or mistake he has made. Actor Jerry Mathers played the role in the pilot and the show's spin-offs.
Beaver's best pals include apple-munching Larry Mondello (Rusty Stevens, November 22, 1957 – June 6, 1960), Gilbert Bates (Stephen Talbot, March 19, 1959 – June 6, 1963), Hubert "Whitey" Whitney (Stanley Fafara, October 4, 1957 – June 6, 1963), and the old fireman, Gus (Burt Mustin, October 4, 1957 – February 24, 1962). Except for Gus, Beaver's friends steer him into trouble time and again. Other friends include Harry Henderson (Keith Taylor), a chubby, bespectacled boy brought in after Rusty Stevens' departure, and Richard Rickover (Richard Correll, April 30, 1960 – October 18, 1962).
Judy Hensler (Jeri Weil, October 4, 1957 – October 15, 1960) is Beaver's snitching, goody-goody classroom nemesis on the show. Penny Woods (Karen Sue Trent, February 20, 1960 – January 20, 1962) filled the nemesis role when Judy was dropped. Other friends include Lumpy's sister Violet Rutherford, (Wendy Winkleman, 1957 and Veronica Cartwright, February 19, 1959 – May 2, 1963). Benjie Bellamy (Joey Scott) and Chuckie Murdock (Rory Stevens) are both small boys and Cleaver neighbors who cause trouble.
Beaver had two female teachers in the earliest seasons. Miss Canfield (Diane Brewster, October 4, 1957 – March 21, 1958) is Beaver's kind and understanding second grade teacher at Grant Ave. Grammar School and appears in four first-season episodes. Beaver has a crush on her in one episode. Alice Landers (Sue Randall, October 16, 1958 – February 17, 1962) becomes Beaver's third grade teacher in the second season, replacing Miss Canfield. She remains his teacher for several seasons. Beaver develops a crush on her but his joy turns sour when she announces her engagement to Tom Brittingham. Cornelia Rayburn (Doris Packer, October 4, 1957 – June 13, 1963) is the principal of Grant Ave. Grammar School and, later Beaver's teacher, after Miss Landers, replacing Mr. Bloomgarten. In the later seasons, Beaver has male, rather than female, teachers who include Mr. Willet and Mr. Blair, both played by Wendell Holmes.
Several episodes in the last seasons concentrate on Eddie's adventures, with one episode following his plans to work on an Alaskan fishing boat  and another chronicling his troubles with a credit card.
Lumpy is the heavy-set, not-very-bright, yet sincere football-playing Clarence, the son of Ward's co-worker, Fred Rutherford. While later appearances would cast him as a friend and classmate, Initially he is an 'outsider' between Beaver and Wally's age. As Beaver's nemesis, he bullies both Beaver and Wally in his first appearance
Wally has several girlfriends through the series' run, with Mary Ellen Rogers (Pamela Baird, occasionally as Pamela Beaird, April 16, 1958 – June 6, 1963) and Julie Foster (Cheryl Holdridge, January 7, 1961 – April 11, 1963) making many appearances. Carol Sydes (aka Cindy Carol) appears as Wally's first girlfriend, Penny Jamison, in "Wally's Girl Trouble", and later appears as classmate and date Alma Hanson.
"Aunt" Martha Bronson (Madge Kennedy, December 13, 1957 – March 28, 1963) is a proper old maid who lives not far from Mayfield and wants Beaver to attend a prep school. She appears in five episodes and is mentioned in other episodes. Because she once gave Wally and Beaver umbrellas, she is called "their umbrella aunt".
Uncle Billy (Edgar Buchanan, December 30, 1960 – March 21, 1963) is Wally and Beaver's fancy-free, globe-trotting, story-telling great uncle. June does not trust him completely because he fills her sons' heads with tales of irresponsible living.
Larry Mondello's mother Margaret Mondello (Madge Blake, June 25, 1958 – February 27, 1960) is a nervous woman who finds her son's misadventures exasperating. The character was dropped when Rusty Stevens left the show in its fourth season. George and Agnes Haskell are Eddie's parents. George was played by Karl Swenson and George O. Petrie. However, in one episode, it is implied that Mr. Haskell's name is "Edward Clark Haskell, Sr."; and in another episode, where he's played by John Alvin, he is "Frank". Agnes was played by Ann Doran and Anne Barton. Tooey Brown's mother, Mr. Mondello, Judy Hensler's parents, and Whitey Whitney's parents make one-time appearances. Larry Mondello's sister in high school is never seen.
Fred Rutherford (Richard Deacon, October 18, 1957 – May 23, 1963) is Ward's pompous, overbearing co-worker. Fred is the father of an awkward teenage son named Clarence ("Lumpy"), and a daughter about Beaver's age named Violet. The Rutherfords socialize with the Cleavers on a couple of occasions: playing cards in the Cleaver home and, at a later time, enjoying a picnic outing together. Fred travels widely and gives Ward a meerschaum pipe after visiting Germany.
Lyle Talbot appeared in two episodes as Mr. Dennison, the father of Beaver's first girlfriend, Linda. In one early episode, Linda is sweet on Beaver and invites him to her all-girl birthday party. Beaver suffers miserably until he sneaks off to a den in the house where Mr. Dennison entertains him with his antique gun collection. Lyle Talbot was father of Stephen Talbot, who portrayed Beaver's friend Gilbert Bates. Talbot had no scenes with his son.
John Hart, the star of the 50s television series The Lone Ranger (54 episodes from 1950 to 1953) and the syndicated Hawkeye and the Last of the Mohicans, appeared in one episode as a scoutmaster. He also appeared in a fifth-season episode as a forest ranger. Hart was father of Buddy Hart, the portrayer of Wally's friend Chester Anderson. Though his son appeared in the scouting episode, the two had no scenes together.
John Hoyt, veteran film and television actor best remembered perhaps for his role as a mad scientist in the sci-fi classic Attack of the Puppet People (1958), appeared as different characters in three episodes.
William Fawcett, venerable performer in countless early television westerns, played Grant Ave. Grammar School's night watchman Mr. Johnson in "Beaver's Crush".
Several Andy Griffith Show players appeared on Leave It to Beaver. Hal Smith, Mayberry's town sot Otis Campbell, appeared as a restaurant manager in the fourth-season episode "Beaver Won't Eat", while Dorothy Neumann, Otis Campbell's wife Rita on The Andy Griffith Show, appeared in "The Community Chest" as a Mayfield housewife. Howard McNear, Mayberry's barber Floyd Lawson, played a barber in a second-season Beaver episode. Burt Mustin (Mayfield's Gus, the fireman) had a long career as Jud Fletcher on The Andy Griffith Show and Will Wright (Mayfield's first season Pete, the fireman) appeared on The Andy Griffith Show as Ben Weaver, a sour, miserly Mayberry department store owner.
Two actors playing veterinarians on the long-running CBS children's series Lassie appeared on Leave It to Beaver. Frank Ferguson (Dr. Peter Wilson in the early seasons of Lassie) played Jeff, the tramp, in "Beaver's Good Deed", and Arthur Space, who portrayed Doc Weaver through the Timmy years of Lassie, played Mr. Judson in "Wally's Present".
Veteran film and television character actresses appearing on the show included Maudie Prickett as Mrs. Bennett, the owner of a lost chihuahua in "Beaver and Poncho", Irene Tedrow as Mrs. Hathaway, Aunt Martha's traveling companion in "The Visiting Aunts", and Lurene Tuttle as Mrs. Evans, Eddie's landlady in "Bachelor-at-Large".
Barbara Parkins, Judy Walker, a babysitter for an older Beaver. "No Time for Babysitters" She understands Beaver wanting to be alone when Gilbert and Richard arrive.