Sangou wasn't the strongest Rider?!
Definitely don't miss this neat little three episode story. A continuation from the Sangou movie.
Thread / Wiki
Also, I've been seeing weird mispellings of the name like Youngo. It's Yon-gou which means 4th one. The gou is just a counter.
Ichi-gou = Number 1
Ni-gou = Number 2
San-gou = Number 3
Yon-gou = Number 4