As a Richard, I imagine, it started as Richard -> Rick. And then someone wrote the R with a real big top part and the lines at the bottom got overlooked.

Got in the wrong government records like that, and soon enough it's a long explaination or you just go with it, and Bob's your uncle.

But rhyming as a sibling notes is more likely (and insinuated by Bob) cockney rhyming slang is insiduious but nickname rhymes aren't quite to the same level.

I'm not going with it, fyi.