|Episode(s)|| 8.13 Everybody Hates Hitler|
12.05 The One You've Been Waiting For
Yeah, well, dropping out of college to wipe out Nazi corpse-bags wasn't exactly my mother's dream, but what are you gonna do?
– Aaron Bass, 12.05 The One You've Been Waiting For
Aaron is the grandson of Rabbi Bass a member of the Judah Initiative -- a secret society of Rabbis which originated in Europe and formed to fight the Thule Society. Aaron is a secular Jew, and he was born in Short Hills, New Jersey.
In the years since the war, Rabbi Bass moved to America bringing the Golem with him. He continued the work of the Judah Initiative and had been trying to find the Red Ledger which recorded necromantic experiments conducted by the Thule for reanimating the dead. He attempts to tell his children, and later Aaron about the Thule Society and his work, but they think they are made-up stories, part of his coping with the horrors of the war. At his Bar Mitzvah, his grandfather gives Aaron a book on how to manage a Golem. Unfortunately Aaron uses the pages to roll joints of marijuana.
Sometime after the death of Rabbi Bass a large box arrived at Aaron's home, and inside was the Golem of Vitsyebsk. Aaron takes the Golem to try to find what happened to his grandfather and find the Red Ledger. Aaron is frustrated that he cannot properly control the Golem. He eventually teams up with Sam and Dean, and they track down the Red Ledger in a college library in Wilkes-Barre, Pennsylvania. A member of the Thule Society, Torvald, tries to take it and shoots poison darts into Sam and Aaron until the Golem kills him and the spell is broken. After incinerating the bodies, Sam works on translating the red ledger and the Golem tells them about when Eckhart destroyed the compound in 1944.
Eckhart, one of the leaders of the Thule Society, and his men track down Aaron and the Winchesters and break in to steal the Red Ledger. Eckhart reveals he can make the Golem inanimate, as Aaron had not written his name on a scroll in the Golem's mouth, which was required for him to properly take possession and control the Golem. When Aaron causes a distraction, Sam and Dean are able to shoot two of the Thule members as well as Eckhart, but one escapes. Before Eckhart dies, he tells them that they will never kill all the Thule.
Sam and Dean offer to store the Golem at the Bunker but Aaron writes his name on the scroll under his grandfather's name and takes responsibility for the Golem, vowing to continue the work of the Judah Initiative. Sam and Dean decided to leave the Red Ledger with Aaron and the Golem to finish what Aaron's grandfather started. Sam is seen updating the library in the Men of Letters Bunker with their copies of the Thule's Red Ledger.
After realizing they may be dealing with the Thule Society once again. Sam and Dean place a call to Aaron, who is currently in Berlin, Germany outside a nightclub. He reveals that he has been making progress in continuing the Judah Initiative's fight, eliminating the Thule alongside the Golem. He reveals that they're halfway through the Red Ledger. Aaron killed six Thules and the Golem killed the rest. When Sam and Dean ask if he has heard anything about the Thule in the States, Aaron tells them that they have mostly been sticking to the "Fatherland", but reveals that he and the Golem got a hold of some Thule documents, telling them of a mission codenamed "Das Blut" -- the blood, where the Thule high command will be all in one place.