Which hero killed Medusa?

The story behind the answer

Perseus is the hero who killed the Gorgon Medusa. Guided by Athena and Hermes, he used a polished shield as a mirror to avoid her petrifying gaze, winged sandals for speed, a curved sword, and a magic sack to carry the severed head. From Medusa's neck sprang Pegasus and Chrysaor. Perseus later used the head to turn the tyrant Polydectes to stone and to save Andromeda by petrifying a sea monster.

To keep it straight: Perseus = Pegasus and petrify. Hercules battled the Nemean Lion and Hydra, Theseus slew the Minotaur, and Achilles was the greatest warrior at Troy. Remember the "P trio": Perseus, polished shield, Pegasus.