Romana (Doctor Who)
Because she was a Time Lord, Romana was able to regenerate, having two on-screen incarnations with somewhat different personalities (called Romana I and Romana II by fans). Romana I was played by Mary Tamm from 1978 to 1979. When she became pregnant and chose not to return for another series, the part was recast. Romana II was played by Lalla Ward from 1979 to 1981.