When Dean and Sam discover the Men of Letters Bunker, Dean decides to help himself to some of the items left behind by the previous tenants – causing Sam to nickname Dean’s grey robe, “the dead guy robe.” The robe is grey, comfy looking, and seems to have the initials T.E.P. monogrammed on the breast pocket. The robe has two large lower pockets too. On January 28, 2016, Ben Edlund confirmed on Twitter that he used a real person as the original owner of the robe - Tyrone Edmund Power - swordsmen, war-time pilot, and film star. You can see the tweets here, here, and here.
In Everybody Hates Hitler (8x13), Dean wears the robe after he gets out of the shower, and talks to Sam about not going all “geek” on the bunker.
In Remember the Titans (8x16), Dean wears the robe at the beginning of the episode when he and Sam are in the bunker.
In I’m No Angel (9x03), Dean wears this robe at the beginning of the episode, when Sam gets back from his run and gives Dean breakfast.
In Just My Imagination (11x08), Dean once again appears in the robe at the beginning of the episode, when Sam discovers Sully in the kitchen. He keeps it on throughout their argument and only changes after he agrees to help Sully.
In Into The Mystic (11x11), Dean wears the robe at the beginning of the episode when he finds Sam in the kitchen cleaning his guns and tells him about the possible case.