Baldomero "Baldo" Bermudez is the title character. A Latino teenager, his primary interests are cars and girls. He is also obsessed with being cool, and is in the middle of an ongoing process to build his own lowrider. He has a job at Auto Y Rod, an auto supply shop (whose logo resembles that of Mercedes-Benz), and according to comic strips in January 2007 and August 2011, he is 15 years old.
Graciela "Gracie" Bermudez is Baldo's younger, Lisa Simpson-like sister. She is an ardent admirer of Frida Kahlo, and frequently attempts to be an activist. She is remarkably smart and enjoys reading, although (in true little sister form) she is a constant annoyance to her older brother. In a May 2009 strip that quotes from the Cinco de Mayo article, Gracie declared that she wrote that article for Wikipedia.
Sergio "Papi" Bermudez, a widower, is the patriarch of the family, the father of Baldo and Gracie, and the owner of a small business. He is often seen by his children as being dorky, although they love him all the same.
Tia Carmen is Baldo and Gracie's ditzy great-aunt. An older woman and very devout in her religious beliefs (she has over 200 religious figurines), Carmen has a vast knowledge and love of old-world customs, foods, and herbal remedies. An April Fools Day gag strip in 2007 depicted her as being detained by the Department of Homeland Security, and a two-week series around the same time drawn in a photo-realistic style told of her as coming to live with the Bermudezes after Sergio's wife Rosa was killed in a drunk driving accident (see below).
Cruz is Baldo's best friend. Arguably similar to Hector from Zits, Cruz is often seen accompanying Baldo in the quest for coolness.
Nora is Gracie's best friend and confidant. She is as bright and intelligent as Gracie.
Beatriz is a young female co-worker at Auto Y Rod. She made a first appearance on the March 5th, 2007. Baldo liked her on a first sight, but later in the strip she told him that she has a boyfriend, although she has since broken up with him. Her appearances have become more common. On the June 17th, 2010 comic, it is revealed that her last name is Ortiz.
Rayna is Cruz's girlfriend. She has a congenitally compromised immune system and can't leave her home, attending classes and dates by means of a telepresence robot.
Ralphie is a friend of Baldo's who owns a lowrider with an advanced sound system. He infrequently appears in the strip.
El Cucuy is the Bermudez family's boogeyman, and is somewhat akin to the snorklewacker from Bloom County. He was forced into retirement after Baldo and Gracie stopped fearing him.
Joey was a semi-recurring Anglo teenager and one of Baldo's former co-workers from a summer job. He had a poor work ethic and was ignorant of the Spanish language and Hispanic culture. Joey's avoidance of work and later promotion to assistant manager frustrated Baldo, but he was eventually fired.
Britney Denise "Smiley" Rogers is Baldo's Anglo ex-girlfriend. She was originally introduced in 2001 as Baldo's new next door neighbor, somewhat plain and tomboyish, with an interest in Latino culture, and was Baldo's girlfriend from 2003 to 2006. Shortly after the breakup, Smiley underwent a sudden makeover and joined a popular girls' clique.
Sylvia Sanchez was deemed the "prettiest girl in school" by Baldo, and the object of his eye from the early strips. She vanished from the strip in 2003, shortly before Baldo and Smiley began dating.
Billy is an antagonistic, subtly bigoted Anglo teen who voices his prejudice against Latinos by accusing them of discriminating against him. Consequently he is disturbed by the emergence of Latino oriented businesses. He is generally a caricature of those who express their bigotry with arguments of reverse discrimination. During a march for immigration rights, he is seen as a counter-demonstrator telling a reporter about the dangers of illegal immigrants.
Smiley's brother is the Rogers equivalent of Gracie. For a brief time, he was Gracie's "boyfriend", but that relationship has since been dissolved.
Mr. Harold was the Gang Activity Monitor at Baldo's school. He had a "tough guy" persona, and falsely accused Baldo of being in a gang after mistaking a game of Rock Paper Scissors for gang signals.
Rosa Bermudez was Baldo and Gracie's mother, and Sergio's wife. Though she has never been seen or heard in the strip (except that her face has been shown in the form of a framed photo), it has been revealed that she had died in a car accident when Baldo was ten years old.  The April 3, 2007 strip—part of a sequence atypically drawn in a realistic style—stated that a car driven by an inebriated motorist collided with Rosa's minivan when she drove Baldo and Gracie from a soccer game. The collision killed Rosa instantly and bruised Gracie. Baldo's soccer ball apparently saved his life in the accident. The April 4, 2007 strip showed Rosa's face (drawn realistically) in a framed photo, while the September 28, 2003 strip had shown her (again in a photo) in cartoon form.
Gregorio who was introduced on the March 26th, 2007 comic, is the one who Tia Carmen has been talking to about Rosa's accident and why she had come to live with Baldo and Family. They met at the tomato section of a store.
Roberto is Tia Carmen's departed husband. Sometimes his spirit visits Tia (in her imagination) for a short time.
Although primarily a strip focused solely on light humor, Baldo has at times delved into political and social subjects relevant to the Hispanic community, such as lottery scams, the 2006 United States immigration reform protests, and greater involvement in improving one's community. Baldo also allows guest artists during Hispanic Heritage month; these guests generally depict Hispanics as crude stereotypes, often harping on low-rider cars and women in very little clothing. This has resulted in both praise and criticism from readers, whose letters have been posted on Baldo's official website and then answered (sometimes sarcastically) by the strip's creators.
In 2009, the strip also dealt with Sergio developing diabetes. Gracie especially reminded Sergio of the need for proper diet and exercise to control his illness, but little mention has been made of Sergio's diabetes after the initial run of strips.
As of 2008, only two collections of the strip have been published in book form.