An informative video taking a look at how the name “Dick” became to be short for Richard.
The name Richard is thought by most etymologists to derive from the Proto-Germanic ‘Rikharthu’, meaning more or less “hard ruler” (‘Rik-‘ meaning ‘ruler’ and ‘-harthu’ meaning ‘hard’). This was adopted into Old High German as ‘Ricohard’, and from there to Old French, then Old English as ‘Richeard’, and today as ‘Richard’.