When Dick Grayson was young, we was part of a 
team called "The Flying Graysons".  With his mother
and father, they together formed the Flying Graysons.

One night, however, everything changed for him, when 
his parents fell to their deaths.  He not only had 
witnessed a man, Tony Zucco by name, inside the tent
where he shouldn't be, but also threatening the owner
if he didn't pay for "protection".

Dick went to stay at Wayne Manor.  He learned about the
ware-abouts of Tony Zucco, and tried a hopeless attempt
to handle him in his own way.  Tony Zucco got away, and
Dick became frustrated, venting his anger out on Batman.
(I'm getting this from "Robin's Reckoning" parts 1 and 2)
Batman then took him to the batcave, revealing his secret.

He then became Robin for numerous amounts of years.  Even
when he was in college, he would help out once in a while.
But he began to grow older, and more frustrated with living
in Batman's shadow.  He wanted a life of his own, and soon
walked out on Batman.  He began to see the world and learn
things (this is from  the Lost Years).  It was when he was 
discovering the world and different lives did he take on his 
own identity as Nightwing.

From time  to time, he comes to help Batman when it gets a
little rough around the edges.  But now, he protects the city
of Buldhaven.  He's grown, still fairly young, and ready for
anything to come his way.