He is described in The Lesser Key of Solomon as follows: The Third Spirit is a Mighty Prince, being of the same nature as Agares. He is called Vassago. This Spirit is of a Good Nature, and his office is to declare things Past and to Come, and to discover all things Hid or Lost. And he governeth 26 Legions of Spirits, and this is his Seal. Joseph H. Peterson - The Lesser Key of Solomon
Vassago is a mighty Prince of Jinnestan ruling over twenty-six legions of demons. He is said to be of the same nature as Agares and is sometimes called the Prince of Prophecy.
Vassago appears as an aged man riding a crocodile and carrying on his right wrist a Goshawk. His eyes are hollow and see into other dimensions, but he is blind in this dimension.
Vassago can be persuaded to tell the magician of events past and future, can discover hidden and lost things, and has a "good" nature.