Aleister Crowley was a complicated character and no 5 minute post would do justice to the intricacies, so, here are the bullet points:
He was an occultist who lived from the late 1800's to the mid 1900's.He was heavily into Qabalah (a form of Jewish mysticism)He joined (and later led) The Golden Dawn and Ordo Templi OrientisHe created his own magical group called the A.AHe was an experimenter with various drugs and MAY have suffered from rather severe addiction later in life
He was an avid mountaineerHe was an author of poetry, fiction, non-fiction and magic/occult booksHe was bisexual, or at least primarily heterosexual (he married women repeatedly throughout his life) and was known to experiment with men from time to time, usually for occult/magic reasons (or so he claimed)
He deliberately played up the reputation given to him by British papers as "The Wickedest Man on Earth" mostly because he enjoyed the celebrity, but he was an opponent of Christianity.
He was extremely intelligent and well known for his wit and very tongue-in-cheek sense of humor
Like I said: bullet points. If you're interested in learning more, I strongly suggest you look out for any of the number of biographies written about him over the last half centruy. I would warn you though. There is a tendency to either totally demonize the man or make him out to be a complete saint. He was neither. He was just a man. Don't take anything written about him TOO seriously and always look for conflicting opinions to try to figure out who the man really was.