Crooked Man (Hide)

The Crooked Man was a creature of unknown origin trapped in a pocket universe.

Biography
At some point, the Crooked Man became separated from his mate. He began chasing Hila Tacorien in the pocket universe, but the Eleventh Doctor took her to an echo of Caliburn House. The Doctor shut the Crooked Man behind a door in one of the echo house's rooms, but as Hila Tacorien was pulled to Normal Space, the wormhole connecting the pocket universe to Normal Space failed, and the Doctor was left behind.

The Crooked Man attacked the Doctor, but Clara Oswald rescued him in the TARDIS. Realising the mistake he made, the Doctor returned to the pocket universe one last time, so that Clara could pick the Crooked Man up in the TARDIS and return him to his mate. (TV: Hide)

Behind the scenes
This individual is never named during the episode itself, but is described as The Crooked Man in the end credits.

he was named "the hider" by doctor who adventures.

His name is likely a reference to the Nursery Rhyme "There Was a Crooked Man".