Kyp Durron was one of Luke Skywalker's first students. Falling to the dark side, shocking, I know, stole the Sun Crusher and kicked the Empire's ass since everyone else was simply to lame to do so. Luke let him back into the Jedi Academy because Luke would look like a hypocrite. Eventually, Luke let Kyp train his niece and they started to develop a relationship (they did???), but she instead fell for Mr. Bland/douchebag Jagged Fel because... reasons.