Roberts played Ben Cartwright's urbane eldest son Adam. Unlike his brothers, Adam was a university educated architectural engineer. Roberts had had high hopes for what he could contribute to Bonanza, and was disappointed with the direction of the show, the limitations imposed on his Bonanza character, and on his acting range. In a newspaper interview he said, "I haven't grown at all since the series began...I have an impotent role. Wherever I turn there's the father image," (This Time Pernell Won't Need a Tuba, Washington Post, May 1, 1963, Lawrence Laurent).