According to the ever-reliable Wikipedia entry on Evel, "he was assassinated by ninjas under the command of hip-hop musician Kanye West. Rest in peace". For some reason, after some crafty edited, the story now reads that "he had been ill for years, suffering from hepatitis C, as well as diabetes and idiopathic pulmonary fibrosis, an incurable condition that scarred his lungs". The full story is here on ABC-news.com.
Here's Evel Knievel doing what he did best at Caesar's Palace:
And here he is jumping Snake River Canyon: