The Other

The Other is a Time Lord from the planet Gallifrey. He was the first ever Time Lord, meaning he was the first able to regenerate. He was banned by fellow Time Lord Rassilon, who wanted to reign over Gallifrey forever. He started travelling and met several Time Lords.

Last adventure and death
After this, the Other couldn't use his TARDIS anymore and was stuck on an empty planet called Floating Island. He tried sending a distress call, which took some time to work, but did work in the end. He was rescued by two people he'd never met before : the Owner and the Doctor.