Pernell Roberts, known to millions as Adam Cartwright in TV western series Bonanza, has died at the age of 81.

The actor, who was the last surviving cast member of the long-running series, also portrayed the title role in MASH spin-off Trapper John, MD.

Roberts initially found fame alongside Lorne Greene, Michael Landon and Dan Blocker as the oldest of Bonanza's three Nevada rancher siblings.

But he shocked Hollywood by leaving the show at the height of its popularity.

The series continued without him, eventually becoming - after Gunsmoke - the longest-running TV western in US history.

Blocker and Landon, who played Adam's younger brothers Hoss and Little Joe, died in 1972 and 1991 respectively.

The actor, who was the last surviving cast member of the long-running series, also portrayed the title role in MASH spin-off Trapper John, MD.

Roberts initially found fame alongside Lorne Greene, Michael Landon and Dan Blocker as the oldest of Bonanza's three Nevada rancher siblings.

But he shocked Hollywood by leaving the show at the height of its popularity.

The series continued without him, eventually becoming - after Gunsmoke - the longest-running TV western in US history.

Blocker and Landon, who played Adam's younger brothers Hoss and Little Joe, died in 1972 and 1991 respectively.

Greene, who played patriarch Ben Cartwright before going on to appear in Battlestar Galactica, passed away in 1987.