Los Angeles , California ( CNN ) -- Actor Pernell Roberts , who played the eldest Cartwright brother in TV 's `` Bonanza , '' died at his Malibu , California , home Sunday at 81 , his lawyer said . Younger TV viewers may remember Roberts from the lead role in `` Trapper John , M.D. , '' a medical drama that aired on CBS for seven years , ending in 1986 . Roberts , a native of Waycross , Georgia , spent much of his adult life `` pursuing his dream of equality for all , '' according to a family statement released by his lawyer , Richard Stone . Roberts spent the first decade of his acting career on stage -- including Broadway -- before he moved to Hollywood to act in movies . His first film was `` Desire Under the Elms , '' starring Sophia Loren and Burl Ives . In 1959 , he landed the role of Adam Cartwright , the handsome and smart son of rancher Ben Cartwright ( Lorne Greene ) in the new western series `` Bonanza . '' His character was serious and introspective , in contrast to younger half-brothers Hoss ( Dan Blocker ) and Little Joe ( Michael Landon ) . The move to a television series `` was a difficult transition , '' the family statement said . `` Accustomed to freely moving from part to part , now being in a wildly popular show , without costume changes , about three grown men living at home with their father , he found did not hold much creative interest for him , '' it said . Roberts walked alongside the Rev . Martin Luther King Jr. in the historic 1965 march from Selma to Montgomery in Alabama , the family said . `` On the set of 'Bonanza , ' he protested the use of all white crews and guest stars , finding some support but never enough to satisfy his sense of outrage , '' the statement said . Roberts left the popular western after the end of the sixth season in 1965 , although `` Bonanza '' stayed in production for another eight years . While the show 's storyline kept open the possibility of his return to the Ponderosa ranch , Roberts never did . He never gained much of a foothold in film , but stage acting kept Roberts busy for more than a decade . He also guest starred in more than 60 TV series . His role of Dr. `` Trapper '' John McIntyre , starting in 1979 , was a spin-off of a character from the hit TV comedy `` M*A*S*H. '' Roberts played the balding physician working in a San Francisco hospital nearly three decades after he returned from the Korean War . His last regular TV job was in 1991 when he was host of the short-lived ABC police anthology `` FBI : The Untold Stories . '' Roberts was married four times . His only son , Chris , was killed in a motorcycle crash in 1989 . His fourth wife , Eleanor Criswill , was by his side when he died Sunday , the family said . CNN 's Brittany Kaplan contributed to this report .
Roberts , 81 , died at his Atlanta home , his lawyer says . Roberts played Adam Roberts , eldest of ` ` Bonanza '' brothers . Roberts was civil rights advocate , marched with Martin Luther King , he says . He 's known to younger viewers as post - M*A*S*H ' ` ` ' '' John McIntyre .