Very clever in hunting vampires. Besides vampires he sees the good in every person (even if others don't), he believes in second chances. Because he has been travelling for so long, he doesn't make a commitment very easily.
Although he is forty he looks more like he is early 30's due to his fit lifestyle. He always wares jeans and tight shirts, because that's easier to fight in.
As a little boy (about 6 years old) he was a witness of a vampire fight (that ended in murder of one of the vampires) trough his bedroom window. But when he told his parents the next morning, they just said it to be a nightmare. Nevertheless he knew it was real and continued to believe.
At the age of 13 he still believed and drove his parents crazy with his believe, so they sent him to a madhouse. There he realized he had to keep his mind to himself to get out. Due to his good behavior he got released after a year.
Although the madhouse released him, his parents still treated him like he was crazy for believing his story for so many years. So he decided to get some proof of the existence of vampires for his parents.
After researching he finds a vampire. The vampire appears to be a vampire who tries to only live on animal blood. After telling his story, the vampire suggest she meets with his parents to convince them of the existence of vampires. He agrees to arranging a meeting, telling his parents they have to meet with his new teacher. Once at the meeting, the vampire kills his parents and then tries to kill him. But during his research he learned about the vampires weaknesses, so he started drinking vervain. In the moment the vampire is surprisingly coughing of the taste of vervain in his blood, he stakes her.
He feels very guilty of being responsible for his parents dead. So at the age of 15 he leaves the place where it all happened and start to travel alone around the world, trying to hunt vampires. So when he abruptly meets a vampire, he starts to attack him without making a plan. Soon the vampire dominates the fight and is about to kill, but then gets saved by ... (the father of Byston).
... takes him under his care and trains him to be a good vampire hunters, together they find the vampire that killed his parent and kill her. When ... and his wife get murdered, Sennar starts travelling again. He didn't stop hunting vampires, but never was able to find and kill the vampires responsible for the dead of ... and his wife.
When Byston finds him, he sees it as his obligation to train him. And together they hunt for the vampires that killed ... and his wife.