Leon Perkins

Doctor Leon Perkins was a human physicist.

He and Dr Irene Schulz travelled in time using a vortex manipulator.

Together they were tasked with procuring a painting from 1899. By mistake they travelled to 1999 and took a painting from a small museum, bringing it back to their client in exchange for a shot for Dr Schulz. (COMIC: A New Beginning)

At some point, Leon's vortex manipulator was sabotaged, and he was caught in a time loop. The portal he was trapped in appeared at various points through time and space, with his hand sticking out and repeatedly uttering the words "grab on! I can't...can't hold...", and also briefly appeared in front of the Doctor at different points in their lives. He appeared aboard the SS Madame de Pompadour in front of the Tenth Doctor, who failed to reach his hand before vanishing, in Amy Pond and Rory Williams's back garden during the Year of the Slow Invasion, without being noticed by the Eleventh Doctor, and inside the lift of the Mondasian colony ship in front of the Twelfth Doctor, Nardole, and. (COMIC: A New Beginning, The Road to...)

Finally, in 3912, the Thirteenth Doctor, Yasmin Khan, Graham O'Brien and Ryan Sinclair saw the portal on Blecplam Two and a Half. The Doctor calculated the space-time coordinates he would pop out next, and there Ryan and Yasmin pulled him out. Perkins was then taken prisoner by the Grand Army of the Just, along with the Doctor and her friends. Once they had escaped, Perkins drew out a gun, and insisted that he needed to take the Doctor's TARDIS. (COMIC: A New Beginning)