Doctor Who: Every Version Of The Doctor Explained

Jo Martin's Fugitive Doctor was discovered hiding in modern-day Gloucester by the Thirteenth Doctor and the fam. 

This incarnation of the Doctor had worked for the shadowy Time Lord organization, Division, which operated outside established Time Lord code. However, the Fugitive Doctor had grown weary of the immoral work she was asked to do. Turning her back on Division, she used a chameleon arch to change her biology and hide out on Earth as Ruth, a charming tour guide.

Ruth lived in Gloucester for an undisclosed amount of time with the Fugitive Doctor's companion Lee, until the Judoon – plus a Gallifreyan operative known as Gat – arrived to bring her in.

The Thirteenth Doctor refused to believe that Ruth was an incarnation from before the First Doctor, but she soon learned that this was the truth.