Ghidorah

Ghidorah is the seventh Pokémon Jacob McKnight gained in Unova.

Unova
Years ago, when Jacob learned of a wild Zweilous was causing trouble for nearby villages, he decided to catch it. Though his Pokémon put up a good fight, Zweilous got away.

Jacob would later get his chance to catch the same Pokémon again, but Zweilous was now a Hydreigon. As a Charmeleon, Smaug put up a good fight even though he was loosing. But soon, Smaug evolved into Charizard and managed to take down Hydreigon enough so that Jacob could catch him.

Following this, Ghidorah wasn't very receptive to Jacob or any of the other Pokémon, and his disloyalty caused problems. After a while, Jacob managed to win Ghidorah's loyalty by showing him that there's more to life then fighting.

Personality and characteristics
Following his capture, Ghidorah was mostly distant from Jacob, scorning his fellow Pokémon and seeking power alone, as well as ignoring the value of friendship, loyalty and kindness. He bore a grudge against Smaug because he defeated him in battle, which bruised Ghidorah's ego.

Once Jacob made the selfless act of taking a Poison Sting from a rogue Scolipede, Ghidorah saw how much Jacob really cared for the Dark/Dragon-type, allowing him to sake off his poisonous personality and became fully loyal to Jacob. Sometime after fighting a battle with Drayden, Ghidorah's ability to work as part of a team was hampered but working together with Goliath, he managed to overcome that difficulty.