Alex Karras, a fierce and relentless All-Pro lineman for the Detroit Lions whose irrepressible character placed him frequently at odds with football’s authorities but led to a second career as an actor on television and in the movies, died Wednesday at his home in Los Angeles. He was 77.

Karras had kidney disease, heart disease and stomach cancer, his family said in a statement announcing his death, as well as dementia. He was among the more than 3,500 former players who are suing the NFL in relation to the long-term damage caused by concussions and repeated hits to the head.

To those younger than 50, Karras may be best known as an actor. He made his film debut in 1968, playing himself in “Paper Lion,” an adaptation of George Plimpton’s book about his experience as an amateur playing quarterback for the Lions, which starred Alan Alda as Plimpton. His rendering of his own roguish personality led to several appearances on “The Tonight Show With Johnny Carson,” and in the 1970s he played numerous guest roles on series television, on shows like “McMillan and Wife,” “Love, American Style,” “M*A*S*H” and “The Odd Couple,” in which he played a comically threatening man-mountain, the jealous husband of a woman who has become friendly with Felix (Tony Randall). Perhaps most memorably, he played Mongo, a hulking subliterate outlaw who delivers a knockout punch to a horse, in the Mel Brooks western spoof “Blazing Saddles.”

In 1975 he played George Zaharias, the husband of the champion track star and golfer Babe Didrickson Zaharias, in the television movie “Babe.” The title role was played by Susan Clark, who became his wife, and from 1983 to 1989, they starred together in the gentle sitcom “Webster,” about a retired football player who takes in a black boy (Emmanuel Lewis), the orphaned young son of a former teammate.

But Karras first earned fame as a ferocious tackle for the Lions, anchoring the defensive line for 12 seasons over 13 years, 1958-70. It was an era when the NFL was rife with talent at the position — Karras’ contemporaries included the Hall of Famers Bob Lilly and Merlin Olsen — but he was an especially versatile pass rusher, known around the league for his combination of strength, speed and caginess. His furious approach — Plimpton described it as a “savage, bustling style of attack” — earned him the nickname the Mad Duck.

“Most defensive tackles have one move, they bull head-on,” Doug Van Horn, a New York Giants offensive lineman who had to block Karras, said in 1969. “Not Alex. There is no other tackle like him. He has inside and outside moves, a bull move where he puts his head down and runs over you, or he’ll just stutter-step you like a ballet dancer.”