For an example - my dad's name is "Christopher." That is what his parents named him when he was born.
However, his older brother was less than a year older than my father. He couldn't say "Christopher." He also couldn't say "baby" correctly. So my uncle *called* him "Bobby."
The rest of the family thought that was adorable and so they started calling him "Bobby," too. (Not just that uncle, but my grandparents, their sisters and brothers, the cousins, the neighbors, and even my dad's younger sisters and brothers)
So he is named "Christopher"
He is called "Bobby"
His father named him "Christopher."
His father called him "Bobby."