Throughout his life, Malthos has always been conflicted with choosing to do good or evil. His adopted family, however, always tried to help others in need, always sought the good in others. They taught him the value of treating others well (karma and whatnot).
While growing up, his family lived in medium sized village where religion was considered very important. He was able to conceal the fact from the other members of the village that he was a Dark Angel, while people may have nearly worshiped him for his angelic half, they would have also sought his destruction if they knew of his devilish half. There were several churches of different faiths -Mostly all dedicated to heavenly deities or angelic beings- in this village, so as he tried several churches, his upbringing led him to the faith of The Angel of Kindness. At least until one day after hunting in the nearby forest for some food, he returned to find his village being attacked by demons, houses on fire, and nearly every person killed. He ran to his families house, hoping that somehow his family might have been spared. What he found was worse than death, he found a demon he thought was only a myth, meant to scare children into submission, he found Kalphistus. Kalphistus had been sacrificing Malthos's family in a brutal ritual to extract their life force and absorb it into himself. Malthos flung himself at the Demon, --revealing his wings and therefore, the fact that he was a dark angel-- enraged by what he saw, but the lesser demons who were with Kalphistus easily held him back. When Kalphistus realized what Malthos really was, he was intrigued. He had heard of tales of Dark Angels who turned the tides in battle, so he offered Malthos a deal, he would spare Malthos if he accepted his offer to join his ranks. Not only that, but he would also teach him and show him immense power. He left soon afterward with the promise he would return the next day to hear what Malthos had decided.
Malthos had never been more sickened by any offer, especially after seeing what the demon had just done to his family. He went to the rubble of the church, not of the church he had been part of for years now (he had forsaken the faith of Kindness after what he had seen that day) but to the church of the Angel of Vengeance, Iaoth. After praying in the rubble of this sacred place, he was surprised to find the Avatar of the Angel Of Vengeance.
Malthos struck a deal with Iaoth to be his servant and sword of vengeance as long as he lived if he could have retribution dealt to those who attack his village.
The next day when Kalphistus returned he found Malthos kneeling, meditating, in what remained of his family home. He had his hordes surround the home and demanded that Malthos stand and give him his answer.
Malthos stood, still facing away from Kalphistus and simply said "You cannot escape from me."
Just as he did, his body erupted in light. Those demons closest to him were burned instantly by this metamorphosis. Wings sprung forth from his back, not the same black, tainted wings from the day before, but angelic wings of pure light. His eyes glowed with that same white light.
Kalphistus growled at the rest of his demons to attack, but several stood as if frozen by fear from what had transpired, but the stronger, more seasoned demons were unperturbed and dutifully attacked Malthos.
Malthos, the new physical embodiment of his patron Iaoth, laughed with a terrible glee as he easily cut down every demon who dared challenge him.
After most of Kalphistus's hordes had perished, he and 10 of his more elite demons attacked. It was a long and hard fought battle, though with Malthos having the strength, stamina and burning desire for vengeance granted to him by his angelic patron, they could not defeat him. The other elite demons fell one by one, Kalphistus seeing this, retreated while the few remaining fought.
When the last of the elite demons had been slain, Malthos rage had abated and Iaoth had withdrawn the full force of his power.
As per their deal, Iaoth had granted him the full use of his powers to wreak vengeance against those who had preyed upon his village (save for Kalphistus), and while Iaoth would never again grant Malthos access to his full power, a portion of his -however relatively small as it would be from this day- power would be available to him throughout his days as long as he kept his part of the deal.
After that battle, Malthos had spent much of his time hunting demons, looking for the coward, Kalphistus to exact his revenge.
Many decades later, Malthos got a lead on the whereabouts of a demon who was supposedly gathering demons and devils to help grow Kalphistus's new army, but when he got to the location the only person there was a noble born paladin of some renown. This paladin had set a trap for any demons or devils who might try to heed the call to arms of a powerful demon.
Because of his half devil heritage, the paladin only saw Malthos as an evil creature and kept him prisoner with his holy magic, he tortured Malthos for information on the Demon Kalphistus, but since he knew nothing about him, the torture continued on. The paladin wouldn't listen to Malthos when he said he was a demon hunter, he insisted "Why would a devil be hunting demons?".
After a few months of Malthos being held captive and being tortured, a daring pirate had heard of this young, rich, power abusing paladin and decided he had found the perfect target of his next raid. He had studied the guards of the young lords manor, planning his heist. He waited until the young Lord had gone to set another trap for any demons or devils, and infiltrated the simple minded guard, and as luck would have it they sent him to help guard the coffers. As he and the guard he was soon going to have to knock out once they took over their post at the coffer were walking, they passed by the dungeon and the pirate saw a person huddled in a corner of one of the cell's. "Hmmm, no one deserves that fate." thought the pirate.
After about 20 minutes the pirate came rushing back through the manor, pockets full of gold and carrying the prize he came here to get. A gem whose value was nearly equal to the cost of the new armaments and lavish furnishings he wanted for his ship. The pirate stopped, however, at the dungeon he passed on the way to the coffers. He looked at the man in the cell and asked
"How would you like a chance to get back at the paladin who imprisoned you?"
"Well, I already took his money, and now I need people to help me spend it... in a manner of speaking anyways."
"Well, I am a pirate you see, and i've recently... Acquired... my own ship. I just need a crew to join me now."
Malthos thought to himself for a moment, then said.
"Aren't you curious as to why a paladin has me locked up?"
"Not really, from my time watching this paladin i've come to realize he's kind of a huge prick."
"Still, he had his reasons." said Malthos as he began to show his blackened wings.
"By my beard!!! Thats freaking Awesome!!"
"So you aren't worried that an offspring of a devil will eat your soul?"
"Nah, i've known a lot of devilspawn, some of them are pretty good guys."
"Ha, well I doubt you know very many good devils, but if you are willing to trust me and my intentions, I will join you."
"Great, you can call me Ironbeard."