Who became the potions teacher after Severus Snape?

He is cunning and ambitious enough to come up with a way to get close to future achievers in order to get free stuff when they become big later in life. He seemed pretty good at picking those with talents. Therefore it made him good enough for Slytherin.

He isn't very brave or loyal so he wouldn't be a Hufflepuff or Gryffindor. He also doesn't seem to thirst for knowledge since he uses others to get where he is in the book so wouldn't be a Ravenclaw, hence the reason he is a Slytherin.

Not everybody in Slytherin was evil or a death eater - it just so happened that many of the characters who were death eaters came from that house. There were probably also a lot of unmentioned Slytherin's who had nothing to do with the Dark Arts. Severus Snape was a Slytherin and a Death Eater but was a spy for the Order of the Phoenix and eventually helped end the war.