In the Fallout TV series, Thaddeus appears to start becoming a ghoul after using a mysterious “healing” substance, but the show has not definitively confirmed his final form yet, and later discussion heavily treats it as an open mystery rather than settled canon.

What actually happens to Thaddeus

  • Thaddeus, a Brotherhood of Steel squire, is badly injured and seeks help from a shady wasteland doctor / snake‑oil type character, who gives him a strange liquid or serum that is supposed to fix his leg.
  • After using it, he develops an inhuman resistance to injury (for example, surviving being shot or severely wounded and then rapidly recovering), which is what leads Maximus to exclaim that he might be a ghoul.
  • The season ends with his condition unresolved on screen, so viewers only see the beginning of a transformation and other characters’ guesses about what he is turning into.

Why people say he “became a ghoul”

  • In‑universe, Maximus is the one who explicitly suggests Thaddeus is “becoming a ghoul,” and that line strongly shaped audience perception.
  • Ghouls in Fallout are known for extreme resilience and slow aging, so his rapid healing and inability to feel pain look, at first glance, like early ghoulification to both Maximus and many fans.
  • Some theorists compare him directly to Hancock from Fallout 4, who became a ghoul by taking an experimental radiation drug rather than just from long‑term radiation exposure, arguing Thaddeus’ mystery liquid might be a similar bioweapon or drug.

The competing theory: super mutant, not ghoul

  • Other fans and commentators argue the serum looks more like Forced Evolutionary Virus (FEV)–related experimentation, which in Fallout lore creates super mutants , not ghouls.
  • Lore‑focused pieces point out that ghoulification usually comes from prolonged radiation, while rapid, dramatic changes from a lab-made serum fit super mutant transformations much better than standard ghoul biology.
  • Reddit and article discussions often frame it as “everyone thinks he’s a ghoul, but the clues actually point to a super mutant or some unique mutant variant,” so there is no consensus in fan spaces yet.

So, how did Thaddeus “become a ghoul”?

Putting it together in one clear line for search/SEO:

  • In the Fallout TV show, Thaddeus begins transforming after taking a mysterious healing serum from a sketchy wasteland doctor, which gives him extreme pain resistance and fast regeneration, leading characters (and many viewers) to believe he is becoming a ghoul, even though later analysis suggests the substance may be related to FEV and could instead be turning him into a super mutant or other experimental mutant.

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