A pot-loving billionaire joins the Giving Pledge

October 25, 2012, 6:54 PM UTC

Peter Lewis in 2010.

FORTUNE — In September, the number of signers of the Giving Pledge (founded by Warren Buffett and Bill and Melinda Gates) grew by 11, to a new total of 92. That’s impressive—92 billionaires each promising (some co-signing with their spouse) to give away at least half of their fortune to charity.

But forget about the raw numbers. The most interesting thing about the expanded list is one of its new members:  With the addition of Peter Benjamin Lewis, the 78-year-old chairman of Cleveland auto-insurer Progressive (PGR), this assembly of very rich and philanthropic souls got its most eccentric participant. Don’t even think of proposing rivals: Nobody could touch Lewis.

Partial proof of that comes with the fact that Lewis’ Giving Pledge letter, posted on the campaign’s website, calls for the legalization of marijuana. That’s a first for the Giving Pledge, which normally mainstreams on education, health and the environment.

But then this is the same Peter Lewis whose riotously uninhibited life Fortune described fully in a 1995 article called “Sex. Reefer? and Auto Insurance.” While that title may offer a broad hint as to how Lewis faces the world, the subject gets absolutely pinned down by an anecdote in the article’s second and third paragraphs, which we repeat.

An investor admiring Progressive’s financial success and just about ready to buy its stock pays a call on Lewis, suspecting him to be indispensable to the company. Getting immediately to his core concern, the investor says, “How’s your health?”

Lewis, then 61, answered in his amiable, straightforward way:  “Well, I really don’t know because I don’t believe in doctors. But No. 1, I feel fine. No. 2, I swim a mile every day. And No. 3, I’m single, so I get laid all the time.”

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This regimen—however ardently it was thereafter pursued—did not keep Lewis from having health problems. In 1998, he had to have part of his lower left leg amputated because of a congenital vascular problem. But that unhappy event becomes part of this story as well, because his pain management strategy in the wake of his operation was to rely on medical marijuana.

He has since forthrightly acknowledged both that fact and his long-time recreational use of marijuana besides. But that was a change: In 1995, when Fortune did its article, he was not yet ready for full disclosure.

We know that because Fortune heard rumors then of his marijuana use—“He is a functioning pothead,” said a friend of his to this writer—and had to ask him straight out what the truth was. He was, after all, the CEO of an auto insurance company, for which various forms of addiction—like drugs—are certainly issues.

Here’s what I said on the phone to Lewis, employing this particular question for the first time in my decades of reporting, “We have heard you are a user of marijuana? Is that correct?”

Lewis answered, “I’m not going to comment.” Later he called back to remind us that a “no comment” is not an affirmation.

But, still, he could have said “no” when we asked–and he didn’t. Even so, we put that question mark behind the word “reefer” in the headline.

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We needn’t have bothered, though it took several years to make that crystal-clear. In 2000, drug-sniffing dogs at Auckland, New Zealand’s airport detected cannabis in Lewis’ briefcase as he arrived in the country to watch the America’s Cup regatta. He was arrested, but was released after pleading guilty and giving $53,000 to Odyssey House, a drug-rehabilitation center.

News stories about that event pretty much eliminated any reluctance Lewis had about publicly discussing this subject he once ducked. Today, he is not only outspoken about his use of marijuana but also zealous in working to see its sale legalized. His compatriots in that drive have sometimes included investor George Soros and University of Phoenix founder John Sperling (neither a member of the Giving Pledge).

But this year Lewis has been the biggest name by far in backing marijuana initiatives that will be voted on in two states. In Massachusetts—where Lewis has given $1.4 million to the cause—the proposal is simply to legalize the sale of medical marijuana. Washington’s initiative, which Lewis has backed with $1.5 million, goes further, proposing to legalize the sale of marijuana to anyone 21 or older. The fate of both initiatives is uncertain.

Meanwhile, Lewis’ pledge letter on the Giving Pledge website stands out even before he gets to marijuana because of an assertion he makes that other people may feel is correct but don’t often state: “Philanthropy,” he says, “is an unnatural act that must be learned and practiced.”

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He moves on to specify—definitely staying in character here—that he likes giving to philanthropies that are “totally honest and open about their intentions.”

And a bit later comes what we will dub, in this election season, the Weed Party platform: “If there is one area,” says Lewis, “that is taboo for most philanthropists yet exemplifies disastrous public policy, it is our nation’s outdated, ineffective marijuana laws. A majority of Americans are ready to change marijuana laws, yet we continue to arrest our young people for engaging in an activity that is utterly commonplace.  I have funded much of the movement to enact laws that give patients access to marijuana as relief for pain and nausea—and have made no secret of being one of those patients myself, using marijuana to help with pain following the amputation of my lower leg.”

Lewis signs off soon after that, in a soulful way that recalls the 1960s. “Take care of yourself. Stay well and happy. Joy, Love and Peace. Peter B. Lewis.”