He is also a Furyan, and urges Riddick to avenge their race's genocide by killing the Lord Marshal. He then promptly commits suicide by walking into the sunlight, in one of the movie's most memorable scenes.
However, it seems to me that no explanation is given as to why he committed suicide. Even if he could not have left Crematoria, he could have stayed behind to be rescued later, or at least waited out his death; there was no need to die at that moment.
Is there an explanation for his action? Perhaps in other media?