Ryu from the Street Fighter series has notably participated in many video game crossovers, such as the Marvel vs. Capcom series, so a Ryu Number can be thought of as a number tracking degrees of separation through character appearances in video games. While the concept of a Ryu Number for game crossovers has been floating around for a while, it appears to have really kicked off with Ryu’s inclusion in Super Smash Bros. for 3DS and Wii U as downloadable content in 2015; for example, this 2016 Source Gaming post provides an extensive list of characters Ryu has directly crossed over with, this 2018 Medium article by Jason Zhen Li directly mentions a Ryu Number, and this 2019 Fanbyte article by Topher Florence calculates Ryu Numbers of some real celebrities, including Kevin Bacon.via the Tumblr’s FAQ
It’s remarkable how close you can get with fictional characters but my all-time favourite is Columbo. Yes, Lieutenant Columbo:
Columbo has an Extended Ryu Number of 4.
Little Richard makes a cameo appearance as himself in “Columbo and the Murder of a Rock Star” when Columbo visits during a performance in a lounge on the trail of a murder suspect. He also voices his animated self in “The Birth of Rock & Roll or Too Hip for the Womb”, the second episode of the 1990 animated TV show Bill & Ted’s Excellent Adventures, where he’s first seen working as a dishwasher in 1995 Macon, Georgia, similar to what he did in real life, except he probably didn’t have Bill & Ted foist onto him a four-year-old Mozart to babysit.
“and THAT, sir,…. gives me GREAT PLEASURE INDEED, Sir!!!”