Dr. Terence Wynn is a character in the Halloween franchise.
His first appearance was in Halloween, telling Dr. Loomis that Michael Myers could not have gotten far because he can't drive a car. Loomis says that maybe someone at Smith's Grove gave him lessons. (This is ironic because it is likely that Wynn was the one who taught him how to drive.)
In the 4-6 timeline, it is revealed that Wynn (often seen walking around as the Man in Black) is the leader of the Thorn cult, and placed the Curse of Thorn on Michael, which is why he is seemingly invincible and wants to kill his family. Wynn was experimenting with pure evil, but as he was planning something with the other members of the cult, Michael grew tired of being used by the Thorn cult, so he grabbed a machete and killed them all. Wynn was killed as well, though his death was never shown onscreen.
It is implied in the room containing baby fetuses and rune translations that Dr. Wynn and his doctors were not really the ancient (possibly extinct) Thorn Cult at all, but merely scientists posing as the Thorn Cult, Wynn cursing Michael to experiment with the Curse of Thorn (which apparently he translated) and performing in vitro fertilization (one such instance being Jamie, which was his first success) in an attempt to clone Michael and spread the curse's evil power. Presumably, Michael's reason for killing them all was because he realized that they were not a real Thorn cult and were using him only for their own twisted experiments.
In an alternate ending, Wynn survives long enough for Michael to attack and swap clothes with him. When Loomis arrives to check on the body and confirm Michael's death, he discovers Wynn who transfers his role as Michael's protector to Loomis, causing his old friend to scream as Michael (dressed in Wynn's clothes) looks back before continuing on. This scene casts considerable doubt on the fates of Michael, Loomis, and Wynn.
Halloween, portrayed by Robert Phalen
Halloween 5: The Revenge of Michael Myers (as the Man in Black), portrayed by Don Shanks, who also portrayed Michael in this film. He killed Sheriff Ben Meeker and the entire police force to set Michael free when he was imprisoned.
Halloween: The Curse of Michael Myers, portrayed by Mitchell Ryan
The remake Edit
In the remake timeline, in Rob Zombie's Halloween film, Wynn's counterpart was a female nurse who was stabbed in the neck by Michael with a fork, portrayed by Sybil Danning.