Stephen Russell, who voices Harold, playes the part of Thief's most loveable characters Benny. The voice that Russell uses is very similar to that of Benny's, if you could imagine Benny rooted to the ground for years. Russell on the Thief wikia.
Deadly Shadows and Fallout utilize a lockpick minigame, where the lock is isolated from the door, infront of a blurry background. In the case of F3, it is a bobby pin and screwdriver.
There is a 'superhero' called The Mechanist, who tries to use his robots for good. The Mechanists in Thief 2 however, are antagonistic.
Russell also voices the Mister Handies in the game. One of the lines it yells in combat is, "Have at thee!" This is what a Hammerite can yell in combat.