Mortigan Goth was made immortal by Mephisto about 800 years ago by winning a chess game against him. Mortigan did this so he could survive the Black Plague that was sweeping through Europe at the time. Eventually Mortigan was tricked into giving up his soul to keep Mephisto from taking the souls of the people of Mortigan's village. The villagers were enraged at this however, as they believed that their deal with Mephisto would have saved them from the Black Plague. They swiftly stoned Mortigan in an attempt to kill him, but his immortality eventually brought him back. When he did awake from his "death", he discovered that the entire village had died from the Black Plague after all. Mephisto then appeared and taunted Mortigan and ended up giving him the name Immortalis. Mortigan swore he'd make Mephisto pay for what he'd done, but Mephisto simply informed him that if he did go against him, he'd simply torture Mortigan's soul a thousand times over, and so he cursed Mortigan to live forever and witness suffering without being able to do anything about it.
Years later, Mortigan found out that Mephisto was torturing his soul anyway, despite the fact he'd done nothing against him. Mortigan therefore started to go against Mephisto in small ways, even teaming up with Doctor Strange some centuries later.
Eventually Mephisto even released Mortigan's soul out into the world, but only because the centuries he'd spent torturing it had ultimately corrupted it into a mere shadow of its former self. Mephisto tasked Mortigan's soul with killing others he'd granted immortality to, and the soul accepted on the condition that he would be allowed to kill Mortigan as well some day. Mortigan eventually encounters his soul in a mirror, and it promptly tears out Mortigan's left eye, which miraculously doesn't grow back. The soul then vows that it will kill Mortigan, but it will do so as slow as possible, making sure to make Mortigan suffer as much as it can. Mortigan becomes strangely at peace with this however, as he now knows that he will actually die one day, something that makes his remaining time all the more precious.
Powers and Abilities
Mortigan Goth is immortal and cannot die, though he can be permanently injured by his own soul.
He is also somewhat skilled in the use of magic.
His blood can cure vampirism for 50 years. Mortigan also has no reflection due to his lack of a soul.