Gary Coleman is most famous for the role of Arnold Jackson on Diff'rent Strokes, a United States sitcom which ran on NBC from 1978 to 1985 and then switched to ABC. He was particularly famous for his catch phrase, "Whatchoo talkin' 'bout, Willis?", delivered to his character's older brother Willis Jackson (Todd Bridges).

Coleman was born with a congenital kidney disease causing nephritis (an autoimmune destruction of the kidney), which halted his growth at an early age, leading to a notably small stature (4' 8") which became his most distinguishing feature. Coleman has had two kidney transplants, one in 1973 and one in 1984, and requires constant dialysis.

During the run of the show Coleman was a popular figure, starring in a number of feature films and made-for-TV movies including On the Right Track, and The Kid With the Broken Halo. The Kid With the Broken Halo eventually served as the basis for the Hanna-Barbera produced animated series The Gary Coleman Show from 1982.

At the height of his fame on Diff'rent Strokes, Coleman earned $70,000 per episode. As he grew older, however, he fell from public favor. After the cancellation of Diff'rent Strokes, his acting career declined sharply. He did play a building code inspector in a Married With Children episode: S08E16, entitled "How Green Was My Apple," where Bundy had called him to report an illegal driveway.

In 1997, Gary did voice work for the The Curse of Monkey Island the third installment in the Monkey Island series of comedy adventure games developed by LucasArts. In 2004, Coleman played a supporting role in the controversial computer game Postal by Running With Scissors, Inc.

He has been featured in one of the seasons of The Surreal Life and was the manager of the Surreal Life characters at the restaurant they worked at. He felt that he was used by the people who made Diff'rent Strokes.

In 2001, he was employed as a shopping mall security guard in the Los Angeles area. A video of him trying to stop a vehicle from entering a compound while the driver (obviously a member of the paparazzi) ridiculed him made the rounds on various late night talk shows. He also cameoed on The Simpsons as himself (in security guard mode).

Coleman occasionally is able to cash in on his camp value to members of Generation X, by appearing in cameo roles in film and TV. As with Day-Glo, Rubik's Cube, Valley girls, Care Bears, Mr. T, the Smurfs and other artifacts from the early 1980s, Coleman's popularity coincided with the childhood of a particularly productive demographic of internet users, and he is, as of 2005, a minor cult figure.

He has also appeared in World Wrestling Entertainment (WWE) superstar John Cena's music video for "Bad Bad Man" in which he appeared as himself, as well as in Kid Rock's video for "Cowboy". In this video he appeared, appropriately garbed, taking on Rock's diminutive sidekick, Joe C. Additionally, Coleman's one-time Surreal Life co-star, Ron Jeremy also has a cameo, as a piano player.

Gary Coleman made an appearance on E's short lived celebrity dating show where washed up celebrities went on blind dates with regular people.

In late 2005 Coleman opened an ice cream shop in Cheyenne, Wyoming called Short Stuff's frozen treats. He is already making plans to expand his business and hopes that he will be taken seriously in the business world.

Gary also appeared in a Nickelodeon sitcom called Drake & Josh. The two main characters were selling a product called the Gary Coleman Grill(a parody of the George Foreman Grill). At the end of the show Gary appears as himself.

In June 2005, VH-1 named Gary Coleman No. 1 on its list of the Top 100 Child Stars Ever.

Gary Coleman is also a character (not an actor) in the hit 2003 Broadway musical, Avenue Q, which won the 2004 Tony Award. In the musical, Coleman is portrayed by actress Natalie Venetia Belcon. The character is loosely based on Coleman himself, or more specifically, on the public perception of him as a child star who lost everything. The character works as the superintendent of the apartment complex where the musical takes place. In the introductory song, "It Sucks to be Me", he states: "I'm Gary Coleman from TV's Diff'rent Strokes. I made a lot of money that got stolen by my folks. Now I'm broke and I'm the butt of everyone's jokes but I'm here, the superintendent, of Avenue Q!" At various times when the Gary Coleman character speaks, theme music reminiscent of an 80s sitcom interrupts the usual Broadway-style music.