Cass Fermazzi

Cass was a human sole pilot from a gunship crashing to the planet, Karn. (WC: The Night of The Doctor)

Biography
Whilst on her way to crashing, she encountered The Doctor, who noticed the ship crashing to the planet and was on his way to save her. She teleported every other pilot apart from herself as she was the only one not panicking. The Doctor offered her the chance to be his companion as they ran to the back, trying to get in the TARDIS. Casswanted to see the universe and was horrified to find out The Doctor was a Time Lord. This altered her desire to travel with The Doctor as she knew of the Last Great Time War and imagined all Time Lords to be corrupt. The Doctor tried to alter her opinion, but she would not accept The Doctor's words, locking herself outside from the room the TARDIS was parked, which was where The Doctor was. Cass preferred to have died than take up the chance to travel with The Doctor. As The Doctor pleaded Cass to change her mind, Cass would allow herself to die.

After The Sisterhood of Karn retrieved both the bodies of The Doctor and Cass, The Doctor was brought back to life in exchange for his services to the Time War. Cass was already dead as the Doctor, before regenerating would talk about how Cass despised The Doctor for who he was.