Phssthpok the Pak has been travelling for most of his 32,000 years - his mission, to save, develop and protect the group of Pak breeders sent out into space some 2 1/2 million years before...
Brennan was a Belter, the product of a fiercely independent, somewhat anarchic society living in, on, and around the outer asteroid belt. The Belters were rebels, one and all, and Brennan was a smuggler. The Belt worlds has been tracking the Pak ship for days - Brennan figured to meet that ship first...
He was never seen again - at least not by those alive at the time.