In another thread, I was reminded of Jeffrey Hunter, who played the lead in the original Star Trek pilot and then declined to film a second pilot, handing the opportunity of a lifetime over to William Shatner. Hunter quickly spiraled into oblivion, and Shatner went on to become, well, Shatner. 
Others, such as Gary Burghoff (Radar O'Reilly in M*A*S*H) and Susanne Sommers (Chrissy Snow in Three's Company) did a bit better after slaughtering their cash cows, but never rose to their original heights.
Do you have any favorites in this category?
Others, such as Gary Burghoff (Radar O'Reilly in M*A*S*H) and Susanne Sommers (Chrissy Snow in Three's Company) did a bit better after slaughtering their cash cows, but never rose to their original heights.
Do you have any favorites in this category?