There's a character in Fallout dating back to the original game called Harold. He's a sorry sight, mutated beyond recognition with a sapling growing out of his exposed cranial innards, but how he got that way isn't clear.
Fans have speculated for years as to whether he's a virus-infected mutant, a radiation-poisoned ghoul, both, or neither, and Fallout co-creator Tim Cain has weighed in on the debate with a larger point: any interpretation is right, so long as it's designated as such.
