First off, if you have the Shaman's Handbook (Green Ronin), consider making him a Shaman. If you don't have a Shaman class, use the Druid.
The spirits always spoke with young Sseeth Lu'Nath, but nobody believed him. The spirits only spoke with the Shaman, never with a hatchling. Still, Sseeth had an uncanny habit of telling everyone when trouble would arise. They never listened, but when the tribal elders would meet later, somebody would always mention the warning that the young lizard had spoken of days before. But, young Ssee knew that they would all believe him one day, oh yes, the spirits told him so.
That day soon arrived when a band of humans assaulted the village. For weeks, Sseeth had been exhorting everyone to retreat further into the marsh before they were all slain, but nobody would listen to the small lizard. Who would attack the peaceful lizardfolk in the marsh? But, the bounds of human hate are endless. It was enough that the lizardfolk lived near to them, the lizardfolk might raid thier town someday. Better to pre-emptively strike. The humans crashed through the huts of the lizardfolk like the wind. The sound of steel slicing through the bodies of his people and their screams of pain hurt his ears.
Even as Sseeth ran for the edge of the friendly marsh, the spirits told him to jump to the side. He did so and the clumsy human, wearing a metal suit, crashed a huge metal sword on the spot that Sseeth would have been. The human snarled and young Sseeth jumped back again, drawing the lumbering hulk toward the sucking mud. Maybe the stupid human wouldn't recognize his danger. It worked and the human blundered into the sucking mud. Without the metal armor, he could have easily freed himself. Even so, he was beginning to struggle free when Sseeth dropped a large rock on his head and then jumped atop the rock. The human couldn't keep his head above the mud any longer and Sseeth smiled as he felt the struggles of the human stop. That was kind of fun, let the marsh take the humans if they tried to hurt him. The marsh would take the humans and their steel and keep the world pure for the lizardfolk. So said the Spirits.
The village warriors eventually drove back the the attacking humans, but the cost to the village was great. The Chieftain was slain and even the Shaman was unconscious from his injuries. Finally, the people listened to Sseeth, just as the Spirits said they would. With uncanny precision, and the help of the spirits, Sseeth guided the remainder of the tribe deep into the marsh, where the humans would not be able to find them.
Years passed, the Shaman acknowledged that Sseeth probably had a Spirit guide of some sort, and tried to train Sseeth as best he could. But, Sseeth was unmanageable. While the Lizardfolk marveled at the steel tools and weapons the humans had, and discussed trying to trade with them, Sseeth railed against the taint of the humans and their corrupting tools. His dislike bordered on fanaticism and his constant exhortations to follow the advice of "his spirits" did little to endear him to the rest of the tribe. The day that some of the younger warriors returned with a steel shield and shortswords, Sseeth flew into a frenzy. The humans were going to corrupt his people, and the fools were willing to help them do so. But, the Spirits had an answer.
A Vision Quest told Sseeth what he needed to know. He must leave the marshes and seek a talking snake that would bring war to the humans, on their own terms. The journey would be long and lonely, but the Spirits would always be there to guide him. Sseeth packed his few belongings, told all that would listen that they were dooming themselves by using the hated steel, that the Spirits and the marsh would devour them if they continued to use the human's tools, and that he would no longer take care of them. He would save them by destroying the humans himself. For their part, the tribe was happy to be rid of Sseeth. Sure, he spoke with spirits, but that was all he spoke with. In truth, he was starting to become a little crazy.
Sseeth left the marshes and wandered the world. He discovered that the marshes were not the only place that would devour humans and their steel. Raging rivers, crushing rocks, even strong and sturdy trees could help eliminate the humans. Even the beasts could be encouraged to help at times. Whenver he found a lone human, he would cleanse the area of the humans taint. Primarily by releasing human's lifeblood in one manner or another. This went on for some time, until a group of bandits caught Sseeth.
With their hated steel weapons, they began to torture Sseeth. Joking about using his beautiful hide as a pair of boots. Sseeth pleaded with the Spirits to help him somehow. Their only answer was to tell him to be patient. It was late in the night when a snake flew over Sseeth as he was staked to the ground. Initially, Sseeth passed it off as a fevered dream as his life was slowly dribbling onto the thirsty earth. But then, a voice called out to the men. As most of them struggled awake, a cone of frigid air engulfed them. Most fell, frozen to death. The snake looped it's coils around the leader and squeezed until he died. The few men left alive were barely able to contain their fear as the snake made itself fully known.
From where he was tied up, Sseeth could just make out the form of a huge snake that had a large humanoid body and head. Even the humans, with their steel, were afraid of thie creature. Sseeth silently asked the Spirits and their whispered responses brough joy to his heart. Yes, isn't this a speaking snake? Isn't it bringing war to the humans and using their own against them? Yes, serve this being and the world will be purged of human taint. Sseeth shouted his greetings to the creature in the tongue of the serpents.
Bothriechis paused in his fury words of greeting being yelled in Draconic at him. His gaze finally caught the tied down lizardman at the edge of the clearing. It was offering service to him. The remaining bandits were a sorry lot. They had been stupid and had disobeyed orders. He had wanted to punish them personally. Now, just when he needed a new leader, a dependable leader, to lead this ragtag bunch, a lizardman offers service. How ... unexpected.
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Perspectives
Sseeth's of himself:
Sseeth operates as Bothriechis' lieutenant. It is a difficult task to interact with the hated humans, but the Spirits assure him that he should use the humans to kill more humans. In that way, the world will be purged of them, and their hated steel. Once this is done, perhaps he can return to the marshes and teach the remaining lizardfolk how to be true to themselves once again.
Of the Bandits that serve Sseeth:
Sseeth is more than a little crazy and the obediance of the bandits under his command has as much to do with their fear of him as it does with their fear of Bothriechis. He constantly mumbles to himself. Rumor has it that he speaks with spirits and reveres Bothriechis as a powerful spirit. But, his spells are useful he doesn't want much loot for himself. Overall, he isn't the worst commander a mercenary has ever had to work for.
Bothriechis':
Bothriechis considers Sseeth to be useful, but ultimately expendable. The lizardman is crazy, but he does have some rapport with some power that grants him spells. Sseeth has a hatred for humans and so long as Bothriechis keeps allowing him to kill humans, Sseeth is controllable.
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Motivations - Sseeth really just wants to keep his people pure. The spirits keep telling him that the way to do that is to kill all humans. If Bothriechis keeps him from his goals, Sseeth will abandon Bothriechis and resume his one-lizard quest. If the PC's can convince Sseeth that he can keep his people pure without resorting to violence, Sseeth would return to the marsh to find a tribe of lizardfolk to live with.
Might be a little shaky. I'm tired right now. But, let me know what you think.