Oscar

Oscar was the pet dog of Sofia Rikkin during her childhood.

A stray taken in by Sofia when she was eight years, Oscar wasn't allowed to stay by Sofia's distant but controlling father Alan Rikkin until after she had begged, making several promises about her grades not slipping and Oscar's behaviour.

One day, while being walked by Sofia, Oscar slipped his leash to go after a squirrel and, overexcited and frightened, bit Sofia as she reached for his collar. Alan was outraged when the pair returned home. He sent Sofia away to his doctor to get stitches then had Oscar, who was Sofia's first connection to a living thing since the death of her mother, shot. Alan later justified his actions by telling his daughter that he didn't like seeing her get hurt.

Reference

 * Assassin's Creed: The Official Movie Novelization