Chugga caught Aron in Episode 13. He named him personally, saying he simply got the idea from the game's ridiculous-sounding Wild Pokémon battle music. He evolved into Lairon in episode 24 after beating Zook, and evolved into Aggron in Episode 39. His type is the defensive Rock and Steel, which is the subject of a running gag.
Chugga once said, "People have been telling me that Billy Bob is a stupid name. To that I say, Billy Bob has the most normal name in all of Orre besides my name!"
Chugga was once upset that the first attack Billy Bob was hit with as an Aggron did 2 damage instead of 1 damage.
At 793 lbs., Billy Bob is so far the heaviest Pokemon Chugga has used.
Billy Bob is the first Rock type Chugga obtained and his second Steel type, the first being Walnut from Pokémon Colosseum.
With a base 180 Defense stat, Billy Bob has the strongest Physical Defense of all of Chugga's Pokémon