Heuler is a serious, reserved dog. He can be hot-headed and he has a bad mouth.
He seems to view wild dogs as slightly lower beings than the ones trained by humans. However, he saves Mel and admits that he and the other Ōu dogs are true fighters. He also helps Smith up with Ken when the old dog jumped to cross the gorge. At times, Heuler speaks and strikes without Jerome's permission. Still, he seems to be closer to Jerome than the other dogs and knows how he thinks. He respects Jerome and also Smith after his sacrifice. When Jerome spoke to Kaibutsu in pain, Heuler told him that the experiment dog wasn't one of them.
Wheeler is one of Jerome's subordinates among the Professional Killers and is the second-in-command. He fights alongside Jerome against Kaibutsu and dies in the fight trying to tear up the monster's weak point to expand the damage further for Jerome, so he could tear the main artery out.
The story of Heuler in the anime is pretty much the same as in the manga, except that Heuler doesn't so clearly seem to be the second-in-command of the Professional Killers. He was the last dog of the Professional Killers to be killed by getting his head crushed by Kaibutsu.
- ホイラー can be written as the German word Heuler and the English word Wheeler. However, Heuler is the official word written in rōmaji in Meishōbu Retsuden, and in the Finnish translation.