Llando had always tried to be a "good" person. He had always done his best to uphold the law, seek peace, and not make undue ripples wherever possible. Of course, that all changed when he freed two of his father's slaves in an act of defiance and abandoned his childhood Telvanni homestead to join the Ebonheart Pact in the war. Even this, though, was an act that Llando inherently believed to be good and right, despite requiring his rebellion against the man who raised him.
Then came Molag Bal. Then came the literal soul-wrenching. Then came darkness and despair. This was the first real taste of suffering that Llando had ever experienced in his life, and most certainly the harshest that would come in quite a while.
Weeks later, when Llando and his companions had returned to the mortal plane, meeting several new allies along the way, he had his first taste of skooma. Of course it had been Fancy Feast who had urged him to "live a little as this one does." Thus began a series of events that would lead Llando to question every ideal he had once upheld as the only "right" way of seeing things. The combination of skooma, his new friends, and his time in Coldharbour had served to completely shake him to his core. This, however, was not what drove him to the darkness.
Eventually, after great tribulations and trials, Llando and his friends managed to defeat Molag Bal--or so it seemed at the time. There was much rejoicing, and the people of the Pact and the Guilds hailed the band of cohorts as heroes--the saviors of Tamriel.
For a time, things were quiet, peaceful, almost normal, even. Llando and his group formed a Book Club to pass the now peaceful days, and maintained under-the-table skooma dealings with a few individuals. During this time, Llando enjoyed wearing bright colors that displayed what his skooma-addled mind believed to be his "aura." He had had his worldview challenged, and had adapted and changed accordingly.
Then Cadwell informed them that their work was far from complete. It all happened so fast--getting shoved into the skin of an enemy. Being forced to live a life of lies that Llando firmly did not believe in. Being forced to aid those who would seek to harm his beloved Pact. Llando was so confused as to why Cadwell would force something so awful on him and his friends, with so little choice in the matter. To make matters even more befuddling, it almost seemed as if they had traveled backward through time to the before they defeated Molag Bal. Dark anchors began appearing again regularly, and foes whom Llando had met in Coldharbour were now alive and well in Tamriel with no recollection of the events that must take place in what Llando can only assume now is the future. Llando was forced to relive battles that he had fought with the Pact on the side of his hated enemies, killing those he had called brothers in arms, and seemingly changing history. Was this all just some cruel joke on the part of the crazy soul-shriven lunatic that Llando had actually at one time enjoyed?
That's when Briolase offered Llando a choice. Apparently, he had been quietly keeping a secret from his friend, but realized that Llando's anguish at the current state of affairs could be remedied with a little bite. Llando readily agreed to something that he would have abhorred only a year prior.
"If I must fight for my enemies," he thought, "then I will prey on them as well, from the darkness. I will weaken them even as I aid them. And I will steal every goddamn thing that isn't nailed down after I finish feeding on them."
Also, he found a panther named Shanaynay who decided to stick around. Panthers are attracted to gothic states of mind.