He is a drafteded Army surgeon called to serve at the 4077 Mobile Army Surgical Hospital during the Korean Conflict. Between long, intense sessions of treating critically wounded patients, he makes the best of his life in an isolated Army camp with heavy drinking, carousing, and pulling pranks on the people he despises, unpleasantly stiff and callous Major Frank Burns and Major Margaret Houlihan.
Although the Robert Altman film followed Hooker's book somewhat in structure, much of the dialogue was improvised and thus departed even from Ring Lardner, Jr's screenplay. The screenplay itself departed from the book in a number of details (e.g. Frank Burns became a major instead of a captain, and was identified with the zealously religious officer that Pierce and tentmate "Trapper" John Macintyre got removed from their tent and, subsequently, the camp) but on the whole left the main characters and the mood intact.
The TV version of Hawkeye proved to be a somewhat different character: While his professional and social life was much the same, he also gradually evolved into a man of conscience trying to maintain some humanity and decency in the insane world he has been thrust into.
Developed for television by Larry Gelbart, the series departed in some respects radically from the film and book. The character of Duke Forrest was dropped altogether and, relevantly to this encyclopedia entry, Hawkeye became the center of the M*A*S*H unit's medical activity as well as the dramatic center of the series itself. In the book and the film, the Chief Surgeon had been Trapper John Macintyre; in the series, Pierce had that honor. In the book and the film, Hawkeye had played football in college (Androscoggin); in the series, Alda's Hawkeye was hardly the football-champ type.
Interestingly, Hawkeye had been married in the book and the film; at the beginning of the series, he was married as well, but references to his marriage were eventually dropped and it was made clear that he was single. Presumably this alteration rendered his romantic dalliances (chiefly with nurses) more morally acceptable in the eyes of Gelbart and the other series officials. (In general, Gelbart tried to make the series less deliberately offensive and more "politically correct" than the film while nevertheless retaining some of its anarchic spirit.)
At the end of the TV series, with the truce, Hawkeye was the last to leave the dismantled camp with the announced goal of returning to his hometown of Crabapple Cove, Maine, to be a local doctor who has the time to get to know his patients instead of the endless flow of casualties he faced in his term of service.