Why do some English first names include a variety of acceptable, yet unrelated, nicknames? (Richard, Charles, James, etc.)

Question

There are so many of these traditional English names that have, seemingly, unrelated nicknames. Who started this and are we still doing it with names today?

In: 1

Answer 1

Also involved are other languages. It took me a long time figure that Jack is a nickname for John (Jon, Jonathan, Johan) because John in French is Jacques. Jack.