"The Dude" is a nickname for Angst's mechanical contraption that follows him around most of the time. In contrast to it stupid looks, T573-DU is capable of storing information, and giving it out via a voice emulator (in completely random phrases, however). Angst invented a device for remembering people's faces, which he tested on his T573.
The argument of whether the Dude has any free will or not is perhaps one of the most heated ones in Dun Garok. The machine gives out tons of seemingly random information, however it makes some sense rarely. To prevent it from being attacked, Angst equpped the Dude with a zapper, and a self-destruction device which will trigger once T573 is taken a large distance away from Angst.
A few more T-573 started appearing in the Brigade, following other Mountaineers.