The demon known as Meg is the daughter to Azazel, and a loyal subject of Lucifer. The demon kept the name "Meg", even after her first meatsuit was killed.
"The yellow-eyed demon and Meg are so much fun to write. The yellow-eyed demon really made his first appearance in 'Devil's Trap'. He was around, but he was never a character who had dialogue and personality. There's a movie called Devil's Advocate, and the sense of humor that Al Pacino brought to his demonic role was great. We really liked the idea that in an episode that's so heavy, let's give the demon a personality and a sense of humor, and a sense of fun - he enjoys what he's doing. Nothing gives me more pleasure than writing one of the demons, because they can be so cruel and so funny; there's nothing they can't say. It allows you to be so mean, but have so much fun with it. Every insult you've always wanted to say, the demon can just say it because that's who he is. Between him and Meg, those two were just really fun characters to write because of how they could talk to the boys and really twist the knife psychologically." - John ShibanSupernatural The Official Companion Season 1, p. 115
There were quite a few articles written how much sarcasm Meg had the first year with Nicki playing her. She did not have time to think about her delivery of her lines as Meg during shooting, but after she stepped away from it, "I actually enjoy watching that kind of sarcasm come out of Meg."Supernatural The Official Companion Season 1, p. 140-141
The actress Rachel Miner was diagnosed with MS and could not continue working. She went to the producers and asked that Meg be killed off, "Fighting the good fight". They honored her wishes, having Meg sacrifice herself to Crowley to allow the Winchesters and Castiel to escape with the Angel Tablet.