Harold is figure from the Fallout series. He was originally a human from Vault 29, from which he escaped in the year 2090. After escaping the vault, he became a merchant, traveling the western wastes of the former United States.
He mainly operated out of the Hub, a major trading city in the west. Some time later, he noticed many caravans never arrived. Angered at the fact that he was losing money, he took a small team on an expedition to Mariposa Military Base in an attempt to stop whomever was killing off the caravans. Most of the team were killed by the creatures and security systems inside. A few, including Harold, made it deep into the base, where they found vats of a green substance: the Forced Evolutionary Virus. Harold was knocked unconscious soon after, and woke up outside the base.
In most cases, when exposed to the F.E.V., the specimen will mutate into a Super Mutant, losing their former personality, memory, and gender. However, in Harold's case, he kept his memories, and also did not grow the the immense size of most Super Mutants. As a result of his exposure, Harold began growing a tree on his head; by the year 2277, while apparently traveling in the Capital Wasteland, he was completely anchored by the tree to the ground. Eventually, plants began springing up around him as a result of the spores released from the tree. When some wastelanders came across it they began to worship him as a god, and Oasis was born.