Rilano is Gavlin old master and mentor. He recruited and taught Gavlin basically everything he knows about crafting and fabrials. He is a high ranking member of the The Diagram and regularly councils with King Taravangian.
He’s been asked to do some things that he’s clearly uncomfortable with, including trying to recruit Gavlin to the Diagram and trying to drain Ravan’s blood to try and trigger a death rattle. After those events he approached Gavlin and apologized and gave him permanent access to Gavlin’s Lab and promised it would be fully stocked and replenished with materials.
Rilano is present when Theren and Ravan approach King Taravangian in his throne room.