PORTLAND, Maine — In 1995 Elon Musk and his brother Kimbal had created a start-up company called Zip2, an online business directory run on such a skimpy budget that they slept at the office, showered at a nearby YMCA and ate three times a day at Jack in the Box.

The business turned out to be good one, though, and four years later the Musks sold it to Compaq Computer. Elon, who was 27, pocketed $22 million dollars. Then he proceeded to show that he was no one-hit wonder. In the years after Zip2 he played a crucial role in creating PayPal, SpaceX and Tesla.

The story of his dizzying ascent is told by Maine writer Anna Crowley Redding in her new biography for young adults, “Elon Musk: A Mission to Save the World.” Her subject is a man of many facets: an inventor, entrepreneur, billionaire, visionary--and the inspiration for actor Robert Downey, Jr., when he first played Tony Stark in “Iron Man.”

Part of the what makes him a fascinating character is that he overcame formidable obstacles, starting when he was a young boy. “He was the smallest kid in his class,” Redding says. “He was badly, badly bullied, even beaten up and thrown down a flight of stairs. He ended up in the hospital.”

What has always set Musk apart from other inventors and entrepreneurs is the limitless scope of his ambitions. He doesn’t just want to change the world, he wants to save it. But he also wants to leave it. “When asked if Elon and Kimbal will travel to Mars together,” Redding writes, “KImbal jumped at the chance to answer. ‘When we are ninety-five, what the hell else are we going to do?’"

Note: Anna Redding Crowley will be speaking at an event at Print: A Bookstore in Portland at 4:00 p.m. on August 4.