Elren is a city elf encountered during the quest Magistrate's Orders in Act 1.
Involvement
Upon arriving at the Abandoned Ruins, Hawke will witness Elren berating the guards for failing to deliver justice to the murderer within. When questioning the elf he reveals that the criminal has been murdering elven children, and implies that he has not received appropriate punishment for his deeds. Furthermore, his last victim was Elren's daughter, Lia. The guards will warn Hawke that defying the magistrate's direct orders is "madness". Hawke can either state his/her intention to bring the criminal back to Magistrate Vanard, as originally promised, or to kill him for Elren. (Hawke can, however, change his/her mind later.)
Result
If you kill the criminal, Elren will thank you and he will reward you with 1 
. If you let him live he will be furious and he will have to move from Kirkwall with his daughter in order to be safe from the criminal.
Later in Act 2 when you go to your new home you'll have a letter from Elren. Depending on how you performed (I killed the "monster") you can receive a letter that mentions his thanks and that Lia "has found a hero in you."