Lex

Lex is from the Species called Guardians, created by The Creator that created the Elementals, It was sent on a mission to capture Dark, but end up meeting The Doctor

Personality
Lex seems to be very calm and collective no matter what the situation is than his "friend" Folker

Missing History
In FF: All The Empty Space Lex was supposed to go Travel with The Doctor but have been replaced with Dark