Volvagia
About
Link first encounters Volvagia when they were both still children. He bought the young dragon from a merchant and decides to keep it as a pet. After some initial antipathy, they became friends.
During the time Link was sealed in the sacred realm, Ganondorf brainwashed Volvagia and transformed it into a mindless monster in order to spread terror across Hyrule. Link and Volvagia eventually ended up fighting each other and Link was forced to kill his former friend.