Ssi was one of the highest deities of the Ssi-ruuvi religion. According to the Ssi-ruuvi holy book, the G'nnoch, Ssi and P'w'itthki hatched from the primordial first egg, while Ssi's offspring hatched from the second egg.
Ssi and P'w'itthki eventually fought, with Ssi winning. Ssi allowed P'w'itthki's offspring to live, on the condition that they serve Ssi's offspring for all eternity. Thus came into being the Ssi-ruu (Ssi's offspring) and their slave race, the P'w'ecks (P'w'itthki's offspring).