G. Gordon Liddy, the undercover operative whose bungling of the Watergate break-in triggered one of the gravest constitutional crises in American history and led to the resignation of President Richard M. Nixon, died March 30 at his daughter’s home in Fairfax County, Va. He was 90.

His son Thomas P. Liddy confirmed the death but did not give a cause, saying only that it was unrelated to covid-19.

A theatrical personality whose event-filled career included more twists and turns than a fictional potboiler, Mr. Liddy was at various times an FBI agent, jailbird, radio talk-show host, best-selling author, candidate for Congress, actor and promoter of gold investments.

The role for which he is best remembered was in the plot to bug the Democratic Party headquarters in the Watergate complex in June 1972.

At the same time, he was viewed by his superiors as “a little nuts,” in Nixon’s phrase. “I mean, he just isn’t well screwed on, is he?” the president complained to chief of staff H.R. Haldeman a week after the break-in.

With his intense stare, cannonball head, bristling mustache and machine-gun style of speaking, Mr. Liddy looked like the archetypal bad guys he later depicted in television shows including “Miami Vice.” His friend and fellow Watergate conspirator, the late E. Howard Hunt, described him as “a wired, wisecracking extrovert who seemed as if he might be a candidate for decaffeinated coffee.”

Mr. Liddy often boasted of his transformation “from a puny, fearful boy to a strong, fearless man” through a regime of intense exercise and physical bravado such as eating rats and holding his hand over a candle until the flesh burned.