In 1965 Pernell Roberts left this series & his part as eldest son Adam, saying he'd grown tired of the role
.... Had left his role on Bonanza (1959), at the end of the sixth season in 1965,... [DOC] [TLE] Pernell Roberts dies at 81; played eldest son on TV's 'Bonanza ... [PAR] Jan 25, 2010 ... Pernell Roberts, a versatile actor best remembered for his portrayal of the ... a 
role he filled from the show's debut in 1959 until 1965, when he left the cast ... 
brother, who played Adam with a suave manner that won a legion of fans.