Withnail

Withnail was cast as an incarnation of the Doctor, alongside his Withnail and I co-stars, in 2008. (NOTVALID: Doctor What 1)

The Ninth Doctor mockingly called his out-of-universe "Shalka" counterpart "Withnail" when he turned him away from the ex-Doctors club. (NOTVALID: Doctor Whoah! 376)

Behind the scenes
Withnail was played by Richard E Grant, a fact directly alluded to in the latter strip.