Vassago is a demon described in demonological grimoires such as the Lesser Key of Solomon and the Book of the Office of Spirits.
Vassago is the third demon in the Lesser Key
a prince "of a good nature" and of the "same nature as Agares".
Vassago rules twenty-six legions of spirits, and is summoned to tell magicians of past and future events, and locate lost objects.
Vassago is one of the few spirits found in the Lesser Key of Solomon but not in Johann Weyer's Pseudomonarchia Daemonum.
Vassago is opposed by the Shemhamphorasch angel Sitael.
Vassago is mentioned in the Book of the Office of Spirits as Usagoo, appearing as an angel, "just and true in all his doings," with the powers of inciting the love of women and revealing hidden treasures, in addition to ruling twenty spirits.
Vassago in invocations to summon spirits that guard treasure,
the "Experiment of Vassago" and the "Experiment of Agares," both intended to capture the named spirits in crystals.
