Lassar

Lucas Finch (properly known as Brother Lassar) was a Krillitane who took over Deffry Vale High School in order to crack the Skasas Paradigm which would make both he and his brothers "gods". He was a very sinister alien and liked eating children for his lunch. Eventually, his plan was foiled and Lucas Finch perished along with the other Krillitanes when K-9 blew up a can of Krillitane oil, destroying both the Krillitanes and the school. (DW: School Reunion)

Behind the Scenes
Finch's first name was not given onscreen, only on the Deffry Vale School website. According to an on-line interview with Head, Finch's original name in the script was "Hector", but this had to be changed when a check found a real headmaster named "Hector Finch". However, Finch's name is given as Hector in the Doctor Who: The Encyclopedia.