Keith's first name is Keith.
Yes it is. It can also be a legal first name for someone.
The letter B and the first letter of his last name.
usually a nickname is a short version of someone's real name. or a name given to someone, by someone else, that has a specific meaning. did you have a certain name in mind?
Keith Bradley
Keith.
Elaine
her name was Elaine.
It may be the name for someone's pet raccoon but it is not used as a nickname for raccoons in general,
If your last name is Rodriguez and your first name starts with a P your nickname is P.Rod
it is a nick name for Elizabeth
Thurgood Marshall didn't have a nickname he went by his real name.