@melbisbelbis
if i remember correctly,
Richard -> Rick -> Dick, Hick
kinda like
Robert -> Rob -> Bob, Hob, Dob, Nob
William -> Will -> Bill, Gill
Basically, from what i gather, there were too many people with the same nicknames, so they rhymed things to make more.
a bit weirder
Margaret -> Meggy -> Peggy
John -> Jen(kin) -> Jakin -> Jack
And then there's
Charles -> Chuck
(apparently, Charles used to be Chukken or something in older english?)
As for Jack and Chuck, i don't really get it, but that's what i found after 10ish minutes of googling