Harold loves explosives, the smell of cordite, and the dull thump of an underground detonation. Grenades or traps, it's all the same to him. He'll plant them, throw them or disarm them. He's earned the nickname "unbreakable", because despite several serious accidents, and living over a hundred years, he never seems to die.
This Harold appears only in Fallout Tactics. Even though he shares the name with a certain other ghoul-like mutant, and has a tree growing out from his head just like him, he probably is just an homage to that character.