Donald Gately is one of the two protagonists of David Foster Wallace's novel infinite jest. Him and the other protagonist, Hal Incandenza, are only mentioned as meeting once, but they are parallel figures and meant to be counterpoints to one another.
Donald Gately (usually "Don", also, as child "Bimmie", for "Big Indestructible Moron"), was born in the early 1980s, making him in his late 20s during the books frame of action, which is probably around 2009. He came from a poor family with an alcoholic mother and an abusive step-father. He became a drinker and drug user during his teenage years, and by the time he was in his early 20s, was an oral opiate addict, a habit that he supported by being a enforcer for a bookie, as well as being a burglar. Eventually, this life of crime and drugs led to a traumatic experience (which is revealed in the closing scene of the novel), and Gately's subsequent embrace of sobriety, through a near-fanatical devotion to Alcoholics Anonymous.
During most of Infinite Jest, we view Donald Gately as his role as alumni counsellor at Ennet House Drug & Alcohol Recovery House, where his streetwise ways, devotion to sobriety and sheer intimidating physical bulk help him keep the various residents of the halfway house in line. Although Gately is uncertain about Alcoholics Anonymous, it has kept him sober, so he is dedicated to it, despite not understanding much of the spiritual purpose he has given himself over to.
During one of the books climactic scenes, Gately is shot and wounded in an incident involving Randy Lenz. Since he is an oral narcotics addict, he can not be given Demerol or any other strong pain killers in the hospital. Much of the later half of Infinite Jest is taken up with the wounded Gately having painful fever dreams and reminiscences in the hospital. At some point, some train of events (probably involving Joelle van Dyne), leads him and Hal Incandenza to try to find a hidden copy of the lethally entertaining movie "Infinite Jest", but how this happens is never described directly in the book.
Gately, as a protagonist, is meant to be a compliment to Hal Incandenza. Gately is poor and intellectually stunted (due to his upbringing and drug use, although Gately is not innately stupid), unlike the privileged, prodigal Hal, but Gately is also capable of faith and action, whereas Hal is emotionally paralyzed. Gately's journey away from drugs, criminal behavior and selfishness is perhaps the crowning narrative and characterization in Infinite Jest, being both moving and realistically portrayed.