The demon Orobas appears in the grimoires Book of Incantations, The Book of Oberon, The Discoverie of Witchcraft, Pseudomonarchia Daemonum, The Lesser Key of Solomon, and Dictionnaire Infernal
From The Lesser Key of Solomon, Crowley/Mathers edition:
Orobas
The Fifty-fifth Spirit is Orobas. He is a Great and Mighty Prince, appearing at first like a Horse; but after the command of the Exorcist he putteth on the image of a Man. His Office is to discover all things Past, Present, and to Come; also to give Dignities, and Prelacies, and the Favour of Friends and of Foes. He giveth True Answers of Divinity, and of the Creation of the World. He is very faithful unto the Exorcist, and will not suffer him to be tempted of any Spirit. He governeth 20 Legions of Spirits. His Seal is this, etc.
Timeline of related events
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1818
Publication of Dictionnaire Infernal (lists this demon)