I've been going through all the seasons of Face Off (which is a contest show with hollywood makeup artists) and I've been getting inspired by a lot of their challenges. I really like their horror movie villain challenges, so I made my own.
The idea is that he is an unstable scientist which obsesses over nature and experiments with plants. He mutated himself by melding with a genetically engineered plant that eats flesh. He thinks all humans should die and 'feed' the earth.