Stren Withel
Stren Withel made his first appearance in The Colour of Magic and was involved in a plot to kidnap and rob Twoflower working with Ymor. He was trained in the Guild of Assassins, but expelled for 'enjoying himself too much' when it came to the inhuming.
He was second-in-command to Ymor, who was described as the greatest thief in Ankh-Morpork. He was ambitious, and nearly killed Ymor at one point, if not for the assistance of Ymor's ravens. This caused Stren to lose his left eye. Stren became the President of the Thieves' Guild.
No known relation to Theda Withel.