Oliver

The youngest brother of Sally and Harry. He is a member of Vert Clan, and last in line to the inheritance, after Serge, Harry and Tom.

Appearance
Oliver is one of the youngest characters in the cast. He is 11 when he first appears in Series 3. He has large green eyes and black hair, slightly longer than Oliver and Harry's, giving him a more childish look.

Family
Oliver is the youngest member of his family. He was very young when his eldest brother, Serge supposidly died, so was less effected by it than the others. He tends to follow his older brother Oliver around, just as Oliver follows Sally.

Villain?
Oliver certainly seems the most unlikely villain of the group. He holds nothing against Harry or anybody else in BASE and is genrally good natured. He disliked fighting, though he can duel with his single sword. He loves animals, especially cats.

In total it is unlikely that Oliver even is a true villain at heart, and much more likely that he'd just going along with Sally and Tom.