The demon Eligos appears in the grimoires The Discoverie of Witchcraft, The Book of Spirits, The Grand Grimoire, Pseudomonarchia Daemonum, The Lesser Key of Solomon, and Dictionnaire Infernal
From The Lesser Key of Solomon, Crowley/Mathers edition:
The Fifteenth Spirit in Order is Eligos, a Great Duke, and appeareth in the form of a goodly Knight, carrying a Lance, an Ensign, and a Serpent. He discovereth hidden things, and knoweth things to come; and of Wars, and how the Soldiers will or shall meet. He causeth the Love of Lords and Great Persons. He governeth 60 Legions of Spirits. His Seal is this, etc.
Timeline of related events
1536Publication of De praestigiis daemonum (lists this demon)
1584Publication of The Discoverie of Witchcraft (lists this demon)
1641Publication of the Lesser Key of Solomon (lists this demon)