By Marjorie Rodrigues

SAO PAULO (Reuters) - During the course of his life, Paulo Coelho spent time in a mental institution, wrote several popular songs and became one of world's best-selling authors with novels like "The Alchemist."

But according to biographer Fernando Morais, that doesn't begin to tell the story of the author's life.

"O Mago" ("The Wizard"), a new biography of Coelho, reveals the wild, sometimes dark, past of the Brazilian writer, Morais said.

"It has everything. Violence, sex, religion, rock and roll, Satanism. And it ends with redemption, because his dream of being a famous writer comes true," Morais said at a news conference in Sao Paulo.

It contains "shocking" confessions Morais said he found in almost 200 diaries and 100 tapes that Coelho, 60, kept hidden in a chest for years.

The 632-page book hit stores this week and sold more than 10,000 copies in Brazil the day it was released. Publisher Planeta plans to release the book in 40 other countries.

"Paulo had so many crazy experiences you almost can't believe it," Morais said. "I felt like Indiana Jones when I opened that chest."

Coelho's wanted the chest containing his diaries to be burned when he died, taking his secrets to the grave. But the author told Morais he could have the keys if he uncovered the name of the man who tortured him during the 1964-1985 dictatorship in Brazil.

Morais fulfilled the task. So Coelho shared his secrets with Morais and the world. Thanks to the chest, the book is full of details about a pact Coelho made with the devil -- later broken -- and his sex life, including three homosexual affairs.

HEADING TO THE SILVER SCREEN

Morais said Coelho's sexual experiences were so shocking that he wasn't sure whether to publish them. In one of the diaries, Coelho describes having sex with his teenage girlfriend in front of her paraplegic relative.

As a teenager, Coelho was placed by his father in a mental institution in Rio de Janeiro. After undergoing sedation and electro-shock therapy there, he fled to northeastern Bahia state, where he met musician Raul Seixas. Together, they wrote several hit songs and experimented with drugs.

"(But) he didn't want to be a songwriter, a journalist or any of the things he did. He only had one dream: becoming a famous writer," Morais said.

The book details how Coelho, during a period of Satanism in the 1970s that included animal sacrifices, made a pact with the devil to become a great author.

The former hell-raiser, who is now a United Nations "Messenger of Peace," is one of the world's best-selling authors.

He wrote 19 books, including "Veronika Decides to Die," that have sold about 300 million copies in more than 150 countries. His latest book, "The Witch of Portobello," was released in 2007.

The biographer said Coelho's life would make "a great movie." In fact, he has already received four offers from Brazilian filmmakers.

Actor Laurence Fishburne is directing a movie version of Coelho's best-seller "The Alchemist," which was released 20 years ago.