Here's a brief look at some of the most notable causes and candidates Lewis championed with his wallet:
* The push to legalize marijuana: "When I was 39 I tried marijuana for the first time. I found it to be better than scotch. But it wasn’t until I had serious medical problems that I realized how important marijuana could be," Lewis wrote in Forbes in 2011. After the amputation of his left leg below the knee at 64, Lewis said he used marijuana in the recovery process. He donated more than $2 million in the 2012 election cycle to help the successful effort to legalize marijuana in Washington state, according to campaign finance reports. He also supported to the effort to legalize marijuana in Colorado.
* John Kerry's 2004 campaign: Lewis invested heavily in trying to help now-Secretary of State John Kerry get elected president and boost Democratic causes in 2004. He donated more than $23 million to liberal "527" groups during the 2004 election, according to the Center For Responsive Politics, including $16 million to the Joint Victory Campaign 2004, an organization that spent big money to try to defeat then-President George W. Bush. That year, Lewis also gave big donations to causes ranging from protecting the environment, to advancing gay rights and reforming marijuana laws.
* CAP/ACLU: Lewis gave millions to the liberal think tank Center For American Progress and the American Civil Liberties Union, including a huge $7 million gift to the ACLU's endowment fund in 2001.