At some point between Fallout and Fallout 2, a small tree inexplicably started growing out of Harold's head. The eccentric ghoul named the plant Bob (sometimes calling it 'Herbert' just to mess with other people), and considered it a good friend, holding conversations with it while he wandered the Wasteland. The tree didn't cause him any pain, so he left it right where it was.
However, the tree would continue to grow steadily over the years, and eventually, it grew so heavy that Harold fell to the ground during an exploration of the Capital Wasteland and could not get back up again. Bob extended roots into the ground and continued to grow, to the point where the plant grew around Harold's body, trapping him in place. Where once the tree had sustained itself on Harold, now the reverse was true; Harold could not move to eat or drink, but the plant fed him through photosynthesis.
As it turned out, Bob is an entirely new species of tree, and its spores are capable of rendering earth fertile, even in the desolate Wasteland. The land around Harold and Bob became green and lush again, and a group of wanderers noticed this and decided to investigate. The relatively uneducated people interpreted Harold's explanation as Harold/Bob being a nature god who would bless the land in exchange for protection. These people, the cult of the Treeminders, formed a community around Bob's roots called Oasis.
At the time the Vault 101 Dweller gets involved, Oasis has thrived for many years, and there is a choice to be made.
Tree Father Birch fears that if Bob's spores continue to spread the fertile land, eventually evil people will notice and come to destroy Oasis and their beloved tree god. He wishes to inhibit Bob's growth by spreading a special salve on Harold's exposed heart. Leaf Mother Laurel, on the other hand, wants to speed up the spread of the spores by applying a special liniment to the heart, believing that if they restore green life to the Capital Wasteland, it will bring joy and peace to every person who lives there. Harold himself, meanwhile, has been stuck in the same spot for decades, and wishes only for the peace of death, which the player would accomplish by shooting the mutant in the heart. It is unknown what the canon choice is, nor what exactly the effect on Bob would be if Harold were to die.
- Harold and Bob were meant to appear in the cancelled 'original Fallout 3', codenamed Van Buren, but in the project bible, the tree was incorrectly referred to as "Fred".
- An organization called the Church of Harold was set to appear in the MMO Fallout Online. It appears to be a more mainstream version of the Treeminders' hippie religion, and Bob features heavily in their teachings.
- In addition to shooting him in the heart, it is possible to kill Harold in Fallout 3 by setting him on fire. This also destroys Bob, and gains the player a pretty large amount of negative karma; this is because, in addition to being a much slower, more agonizing death than simply being shot, Harold is actually terrified of fire.