Ted is a very non-specific character in Dilbert. He is referenced to by Alice, Dilbert and Wally as unproductive and unintelligent. Usually when he appears, he is getting fired. Ted is almost always different when he appears, sometimes he'll come back with different faces or just as a different race all-together. In one story arc of Dilbert comic strips in which Catbert spray painted a letter on his chest every week before firing him, he had dark skin. After being fired in that story arc, he appeared a few weeks later as a white guy with a different face only to be fired again. To be fair, the other characters have slowly changed their appearance over the years and have had loose continuity like getting fired and coming back, but not as often or as suddenly as Ted.
In Y2K, he was listed in a book of employees Catbert was planning to fire. The book says that "there may be more than one Ted." Later in the episode, Ted told Dilbert angrily that he was not the Ted he was thinking of.
Creation and Evolution of Ted
Ted typically only appears when Scott Adams needs a placeholder character for a scene. Due to Scott Adams limited artistic range, a lot of the placeholder characters wound up looking like the same people. Scott Adams privately gave him the name "Ted, the Generic Guy," though he may have other names in the comic.