Robo-Fiend is Ultra Lord's arch-nemesis.
It's revealed that Robo-Fiend is lactose intolerant, which is how he got defeated in the episode, Ultra Sheen. Sheen prompty then uses llama milk to spray all over his face, forcing him to yell "No! I'm allergic!" He then runs in agony and explodes into pieces in the distance. This weakness of his was never brought back up again.
- Despite the fact that Robo-Fiend is lactose intolerant, he is a robot and therefore, non-organic in a sense. Although it is possible that liquids make him malfunction.
- Although Sheen states that Robo-Fiend is lactose intolerant, he yells out that he's allergic to milk. It is unknown which of these is true, or if both are applicable.
- Robo-Fiend has an on/off switch on his back, which deactivates him whenever Sheen touches it.
- In the episode Send in the Clones, Sheen was playing with an action figure of him and Sheen was making him say to Ultra Lord "You can't catch me!"
- The evil clone version of Sheen is a fan of Robo-Fiend and dislikes Ultra Lord. Ironically, Evil Sheen is still wearing an Ultra Lord shirt instead of a Robo-Fiend shirt.