The brilliant but socially inept Dr. Bartholomew was a horticulturist and chemist killed in a laboratory accident only to be resurrected more plant than human through the intervention of his experimental plants. His mind, twisted by the mutation, constantly wavers between that of an eco-terrorist resorting to crime as the means to an end and a criminal outcast enslaving the plant life he claims to understand as his "army" against a foolish humanity.
Greenthumb is one of the five criminals set free by the mysterious Flux.
After noticing a delivery truck of plant life while investigating the construction of the Sunspire Tower Peter Grey and Stiletto break into the Noctropolis Greenhouse. There they encounter Greenthumb lying in wait for them and Stiletto is knocked unconscious by enormous mutated sunflowers while vines wrap around Peter Grey's limbs, immobilizing him in the air, their poisonous thorns piercing his skin.
- He closely parallells several DC Comics characters including Swamp Thing, Poison Ivy and The Floronic Man and bears some resemblance to The Weed seen on The Plastic Man Comedy Adventure Show and Solomon Grundy. He also resembles Marvel Comics' Plantman aka Blackheath.