Fourteenth Doctor

Bold, curious, and youthful, the Fourteenth Doctor was by far one of the sweetest incarnations of the Doctor – as well as the youngest physically – a result of his previous incarnation's positive view on life.

A new body
After being fatally wounded in a battle, the Thirteenth Doctor regenerated into the Fourteenth. Immediately following his regeneration, the Doctor landed the TARDIS in what seemed to be modern-day London. He stepped outside of the TARDIS and promptly fainted outside of St. Luke's University. (TV: The Dimension of the Lost)

Post-regeneration
The Doctor entered a post-regenerative haze, requiring a place to stop and recuperate while the TARDIS recalibrated. Subconsciously, the Doctor returned to the office that his past incarnation had inhabited, only to find that it had been occupied by Professor Talia, who taught Creative Writing, and had just finished a meeting with student Louis Wintercrest. The two bumped into each other, and the Doctor asked if the Doctor was still at the university. Though he wasn't, Louis knew of the Doctor, and wanted to know more about him and his mysterious disappearance after 2017. He also noted that there was an attack by something creepy back in 2019 by a 'bloke called the Doctor'. Louis theorised that the Doctor was a role rather than a person. Not remembering fighting anything at the university in 2019, the Doctor used a vortex manipulator he had ordered directly from UNIT to travel back to 2019. After encountering the Solitude, the Doctor sent it to 2022. With the help of Louis, the Doctor defeated the Solitude, banished it to the Dimension of the Lost, and offered Louis a spot in the TARDIS. He and Louis entered the TARDIS together, and the Doctor liked its new console, which was much brighter and vibrant. (TV: The Dimension of the Lost)

Personality
Differently from his more recent predecessors, the Doctor was shyer, but wore his heart on his sleeve, confiding in Louis Wintercrest not long after they had met. He was also very inquisitive and quick-thinking, able to figure out mysteries relatively quickly. This new incarnation was charming, appealing first to the Solitude's sense of loneliness before realising that they were not willing to negotiate. In this vein, he was much like the Tenth Doctor, only giving his enemies one shot. (TV: The Dimension of the Lost)

Appearance
The Fourteenth Doctor had a very youthful appearance, seeming physically to be only in his 20s. He had light brown hair which he kept brushed back, and smiled constantly. After changing out of his predecessor's clothing, the Doctor began donning a red-and-black checkered flannel shirt, a denim jacket, a black vest, and jeans, basing his style off of companion Louis Wintercrest. (TV: The Dimension of the Lost)