Soul Calibur III
In his first appearance, Zasalamel acts as an antagonist rather than a hero.
Like many characters in the series, Zasalamel seeks to obtain Soul Edge, but also Soul Calibur in order to make himself mortal. Although his goal is not necessarily evil (as most villains would seek the opposite benefit), he sought to do it by eliminating the Soul Calibur III's character creation by battling them inside the clocktower and later during the final battle, where he transforms into Abyss.
Once Abyss is defeated, the player has the choice of whether to cure him, or leave him to die.
Soul Calibur IV
In his second appearance, Zasalamel is revealed to be alive whether or not the player from the previous game killed or spared him. This time, he seeks to find the swords once more, but not to become mortal, rather to preserve reality.
Zasalamel takes on a more anti-heroic role, where he defeats the Hero King Algol and absorbs the power of the swords with a green orb, trapping their power so that they can't be manipulated once more.
Four hundred years later in present-day Los Angeles, California, he is a successful billionaire and philanthropist who continues to observe over humanity.
Soul Calibur VI
Zasalamel's most heroic role occurs in his third appearance.
In the Libra of Souls storyline, Zasalamel is the first character the player comes across, he tells them that a major and dangerous quest alies ahead for them, but also warns that the choice they make along the way will affect the course of events. After telling them a brief (and obscure) backstory of what's going on, he gives them the Libra of Souls, a set of balancing scales with one end with a red flame (representing evil) and the other with a blue flame (representing good), which serves as the representation of the protagonist's alignment. He then disappears.
He can be encountered in northern Spain where he shows the protagonists the effects of the Evil Seed, where he witnesses the protagonist battle a group of malfested.
After Azwel is found to be alive after seemingly surviving a certainly fatal fall. He tests the protagonist's fighting skills against his own to see if they are ready to confront Azwel, once he is defeated by them, he wishies the protagonist good luck in their fight to kill Azwel and save the universe, and tells them that when the right moment arrives, they will be able to summon either Soul Edge (if they are evil) or Soul Calibur (if they are good) using their will.
Once the main storyline is completed, Zasalamel will confront the protagonist in Scandinavia where he will test the protagonist's endurance and again in the Middle East, where he will challenge them to the final test against him using all their power, once he is defeated in this battle, he will send the protagonist back to the very spot the protgonist started in the storyline, and pretends to make them believe that time has reset, before revealing that this is not the case, and leaves them to continue their life in peace, wishing them a final farewell.