Petra was a female mixed breed dog that appeared on the BBC children's programme Blue Peter between 1962 and 1977. She was the first Blue Peter pet, and remains one of the best known. She had several puppies, including Patch, who also became a Blue Peter pet, and who predeceased her.
Petra Kristensen is a fictional character, a mutant appearing in the comic books published by Marvel Comics. She first appeared in X-Men: Deadly Genesis #1. Petra was created by writer Ed Brubaker and artist Pete Woods in the limited series X-Men: Deadly Genesis and was one of the "Missing X-Men".