Magus - attains to Wisdom, declares His Law (See “Liber I vel Magi”) and is a Master of all Magick in its greatest and highest sense.
The Grade of Magus is described in “Liber I vel Magi,” and there are accounts of its character in [The Vision and the Voice], in the Higher Æthyrs.
There is also a full and precise description of the attainment of this Grade in the Magical Record of the Beast 666.
The essential characteristic of the Grade is that its possessor utters a Creative Magical Word, which transforms the planet on which he lives by the installation of new officers to preside over its initiation. This can take place only at an “Equinox of the Gods” at the end of an “Æon”; that is, when the secret formula which expresses the LAW of its action becomes outworn and useless to its further development.
(Thus “Suckling” is the formula of an infant: when teeth appear it marks a new “Æon,” whose “Word” is “Eating.”)
A Magus can therefore only appear as such to the world at intervals of some centuries; accounts of historical Magi, and their Words, are given in Liber Aleph.
This does not mean that only one man can attain this Grade in any one Æon, so far as the Order is concerned. A man can make personal progress equivalent to that of a “Word of an Æon”; but He will identify Himself with the current Word, and exert His Will to establish it, lest He conflict with the work of the Magus who uttered the Word of the Æon in which He is living.
The Magus is pre-eminently the Master of Magick, that is, his Will is entirely free from internal diversion or external opposition; His work is to create a new Universe in accordance with His Will. He is the Master of the Law of Change (anicca).
To attain the Grade of Ipsissimus He must accomplish Three Tasks, destroying the Three Guardians mentioned in [The Vision and the Voice], the 3rd Æthyr; Madness, and Falsehood, and Glamour, that is, Duality in Act, Word and Thought. (from "One Star in Sight")