Titans were the first of the powers to exist in physical form. Titans are the living, physical manifestation of their world.
There is never more than one titan found on any world. However, they can carve parts of themselves off to serve specific functions. In this way a world could be populated by a swarm of seemingly different entities that are in fact just parts of a greater whole.
The link between Titans and the emergence of the Gods is well known. On worlds where the resident Titan has fallen, and life has taken hold, certain creatures may collect the power of the Titans and become much more than they would normally be. These beings, are generally known as gods. Where titans still walk their worlds, no god ever spontaneously rises.
It has also been suggested that the Titans propagated life throughout the realms, either deliberately or by accident. Those favouring the idea of a deliberate spread argue that life somehow generates additional mystical properties that are inimical to Celestial life. Others are less romantic, claiming that life was tracked accidentally from one realm to another like mud on a shoe.