Sao Til

Sao Til is an alien being once met by Jack Harkness in the TARDIS.

It was later revealed that Sao Til was actually Tim Ingham roleplaying an alter-ego, he wore a blue mask, a black bowler hat and a huge robotic arm. John Barrowman was also roleplaying his famous character Jack Harkness in the TARDIS set. They had a faux-battle, before they were interrupted by David Tennant, who asked them to get out of "his TARDIS". (NOTVALID: Tonight's the Night)

Behind the scenes

 * According to the Sao Til website, his name, when combined with that of his species, Aminopius, was intended to create an anagram of animus spoliatio, Latin for soul robbing.