What Silicon Valley legend creates "custom" versions of US currency that are totally legal to spend?

Image by ericskiff via Flickr

On July 14, 1969, The United States Federal reserve removed from circulation any denomination of US currency larger than the $100 bill. While the $500, $1,000, $5,000, $10,000 and $100,000 bills are still valid currency, they are rarely spent, as any such bill that makes it into the Federal Reserve system will be retired -- and these rare bills have collectible value well above their denomination.

Still, some idiots just can't resist counterfeiting large and/or fictional denominations of US money, even though they're almost invariably caught trying to pass these bills off. What's even more shocking are the imbeciles that try to pass these fake notes off at Las Vegas casinos -- perhaps the single most counterfeit-aware group of businesses on the planet.

Thus it's apropos that Vegas gave the most trouble to a legendary Silicon Valley businessman who creates unusual -- but perfectly legal -- "custom" versions of US currency.

What Silicon Valley legend creates "custom" versions of US currency that are totally legal to spend?