Originally Hekademos, occasionally Academus, usually Akademos.
Well, the first time Helen of Troy was abducted (she was still Helen of Sparta, at that point) she was only 12 years old. At that age, it's not your husband who comes after you, it's your brothers (or brother and half-brother, in Helen's case). So Castor and Pollux (AKA Polydeuces) went off on a quest to get her back. But on arriving in Attica, they realized that they just didn't know where to go next.
Enter Akademos -- a farmer. Akademos reveals to Castor and Pollux the location where Theseus had hidden Helen (he had left her in the care of his mother, until she would come of age). I have not been able to find out how Akademos knew where Helen was, but his knowledge spared the surrounding countryside from being ravaged by searching troops.
In return for his help, Apollo granted him a garden wherein he could say anything he wished -- even things against the gods -- without retribution. This was the Akademeia located near Athens. Because of this association with the Dioskouri (that's Castor and Pollux), the Spartans spared this bit of land during their invasions, along with the schools that sat on it. This grove became the site of Plato's favorite teaching spot, giving rise to the words academy, academic, academia, and other related words.