Oliver Seidel

Oliver Seidel was the chief antagonist of the Angel episode "Supersymmetry" and was a genius lecturer who also had a nasty habit of spiriting away any students he felt were a threat to his own power via the use of dimensional portals that led to strange hell-dimensions: his most famous victim was Fred.

Late 90s
While a physics professor at UCLA, Seidel, sent many of his students who he believed posed a threat to him to other dimensions via portals, including Fred Burkle. Seidel's TA for High-Energy Physics was Laurie Drummond while Fred was his student and remained in that position until Seidel died.

After Fred's Return
When Fred was asked to present a paper she had written on the subject of supersymmetry to the Institute, Seidel won the honor of introducing her. During her speech, he opened a portal above her from which a multi-tentacled demon emerged and tried to kill Fred. It was defeated by Angel and Gunn. Later, while alone in Seidel's office, Fred discovered that Seidel was responsible, at which point she went to Wesley for help in killing him. After another attempt by Seidel to send Fred away, she opened a portal to a hell dimension, through which she intended to send Seidel. Before she could carry out her vengeance, Charles Gunn broke his neck and then threw him in, hoping to save Fred from having to commit such a deed herself.