He was voiced by Tim Curry.
When Duckman and Chicken were children, Duckman bullied Chicken into becoming the most unpopular kid in school. (However, in the episode "Cock Tales for Four", it was revealed that Duckman did so to keep himself from being bullied as he was once Chicken left school.) This motivated Chicken to a life of plotting revenge against Duckman and would usually show up as a motivation rant in each of his appearances-usually parodied by Duckman and those who tired of hearing it.
At some point, he met and married Honey, a busty, attractive, unbearably beautiful and insanely sexy Southern-accented bird woman with a drinking problem and had an unseen daughter named Tammy who briefly dated Duckman's son Ajax. However, King started to have relations behind her back with Duckman's sister-in-law Bernice until their eventual divorce.
Generally, King Chicken tries to form plots that would result in Duckman being utterly humiliated and isolated in the process, if not also outright killed. Chicken works as a master of disguise, typically hiding as a human character setting up a plot to ensure Duckman's humiliation and possible death. (Though generally, hearing a character voiced by Tim Curry in Duckman is a giveaway of Chicken's disguises.)
In one such instance, he posed as a fake French nanny for Duckman's sons and triggered a mass contempt for the fowl by portraying Duckman giving "her" an apple as a crude, sexual act. This plot led to Duckman being attacked and oppressed by groups of feminists (although Duckman's general behavior did not help). In another, he posed as a salesman of a beauty product that would allegedly make anyone beautiful but would cause any matter it touched to dissolve away, using Duckman's former girlfriend Angela as a pawn. Although knocked into the dissolving product, he was healed by the antidote although he looked like Duckman. He returns to normal as times goes on.
By the end of the series, Chicken manages to put aside his differences while planning his wedding to Bernice (as well as Cornfed planning his wedding with Beverley and Duckman with Honey). But whether or not this truce of sorts lasted is unknown as the series reaches an abrupt inconclusive ending with the appearance of Duckman's thought-to-be-dead wife Beatrice.