Fan Casting The MC-Whoniverse

During the battle against Ultron in Sokovia, the Avengers come across a strange man in a blue Police Box, named the Doctor. He is from another universe, but got stranded in the world of the Avengers on accident. Stuck in this new world, he works with the Avengers and other heroes to protect this world from the dangers that it faces. The truth begins to unravel, however, and soon the Doctor learns there is a much darker force at play. One that could lead to the destruction of both worlds. *Timeline-Wise, includes 'Age of Ultron', 'GOTG Vol. 2', 'Civil War', 'Doctor Strange', 'Spider-Man: Homecoming', and other original stories throughout. *Exact incarnation of the Doctor has not been determined. In my mind it is Peter Capaldi, but could be reworked for any version, as the Doctor does not have a pre-established companion with him throughout the story.