The Immortal is a terrifying creature unleashed by Stupidhead1836 (aka me). The only thing the Western pack know about it is that it has destroyed a large number of packs, taking zero prisoners.
Not much can be concluded about the Immortal's personality because, to the average wolf, it would be very difficult to make anything out of it.
As Runt later discovers, the Immortal doesn't always act like what its name suggests. In fact, he found that the reason why it destroyed all those packs was because, to it, it was actually making them happy. That might confuse the average wiki user, but all you really need to know is the term schizophrenia. That one word describes the Immortal in a nutshell. Runt often saw it chasing butterflies, and found out it was scared of spiders. It also played with Runt instead of trying to kill him, as the other pack members thought. This made the Immortal seem more like a pup than a monster, which it is.
The Immortal is a cat-dog hybrid covered from head to tail in a suit made of something that feels stretchy but can withstand even the hottest of fires. It's face armor has a menacing appearance with eye holes that look black but can reflect light. There is a log-like thing on its back that is black in color. Its suit is also black allowing it to blend in with the dark.