Ian was a hunter and owner of a shop called Ian's Herbal Remedies in Ogden, Utah. His shop also served as a haven for hunters, as noted by the special "hunter's signs" on the door. His shop is used by hunters to procure certain ingredients and presumably other paraphernalia for hunting and spells. Sometime in the past, he helped Sam and Dean out while they were hunting a witch.
The Winchesters and Castiel find out that the angel Gadreel is moving north, and believe he will end up next in either Auburn or Ogden, Utah. Dean sends Castiel to Auburn while he and Sam take Ogden. The brothers remember once getting help from Ian last time they worked on a case there.
As Sam and Dean race to Ogden, Gadreel enters the store looking for griffin feathers and fairy bones, telling Ian knows about the hunter's signs on his door, which lulls Ian into trusting Gadreel. By the time Sam and Dean arrive, they find Ian's dead body hanging on a door with his eyes burned out.