I've seen several people on here ask questions about nicknames before, so I was going to post a wonderful link about nicknames for anyone who was interested... but it was a geocities site, and geocities is no longer available. D: I'm very distressed! So I thought instead I would just give you all of the information I can remember about some types of English nicknames.
When the Normans came to England they brought a lot of Latinate names. The Anglo-Saxons couldn't pronounce Rs very well, so they changed the Rs in names to other consonants to make nicknames. Examples:
Mary-->Molly
Sarah-->Sally, Sadie
Margaret-->Madge, Meg, Mamie
Caroline-->Callie, Caddie
Dorothy-->Dolly, Dodie
Harry-->Hal
Similarly, some nicknames come from Rs being dropped. Examples:
Florence-->Flossie
Frances-->Fanny
Dorothy-->Dottie
In the Middle Ages it became common to alter the first letter of a nickname to make a new nickname. Examples:
Mary-->Molly-->Polly
Margaret-->Meg-->Peg
William-->Will-->Bill
Robert-->Rob-->Bob
Richard-->Rick-->Dick
Also in the Middle Ages, a term of endearment was to say "Mine" before the name. In some cases the "Mine" was dropped, but the N was left to form a new nickname. Examples:
Oliver-->Noll
Edward-->Ned
Abel-->Nab
Anne-->Nan, Nancy
Helen, Ellen, Eleanor-->Nell
Another form of nickname used in the Middle Ages was adding "kin" to the end of a name. Many of these nicknames aren't used anymore, but some were altered slightly and are still in use (and some are now surnames, I guess). Examples:
John-->Johnkin, Jenkin-->Jack
Henry-->Hankin-->Hank
Robert-->Robin
Nicholas-->Colin
Charles-->Chuck
Peter-->Peterkin, Perkin
Walter-->Watkin
Thomas-->Tompkin