Marbas

Marbas, who customarily appears as a roaring lion, but who, if the magician requests, will happily assume human form.  He can offer the same shape-changing ability to men.  In addition, he can answer questions about anything hidden or secret, and cause - or cure, if he chooses -  disease.  (c)

Marbas, alias Barbas is a great president, and appeareth in the forme of a mightie lion; but at the commandement of a conjuror commeth up in the likenes of a man, and answereth fullie as touching anie thing which is hidden or secret: he bringeth diseases, and cureth them, he promoteth wisedome, and the knowledge of mechanicall arts, or handicrafts; he changeth men into other shapes, and under his presidencie or gouvernement are thirtie six legions of divels conteined. (g)

MARBAS.—The fifth Spirit is Marbas. He is a Great President, and appeareth at first In the form of a Great Lion, but afterwards, at the request of the Master, he putteth on Human Shape. He answereth truly of things Hidden or Secret. He causeth Diseases and cureth them. Again, he giveth great Wisdom and Knowledge in Mechanical Arts; and can change men into other shapes. He governeth 36 Legions of Spirits. And his Seal is this, which is to be worn as aforesaid. (h)

Resource List - all entries are taken verbatim from the original source:

(c) "Fallen Angels...and Spirits of the Dark" by Robert Masello ©1994. 

(g) Pseudomonarchia daemonum - Johann Wier (1583)

(h) The Lesser Key of Solomon.  GOETIA.  Compiled and Translated By S.L. "MacGregor" Mathers.  Editing and Additional Material By Aleister Crowley