Spoilers if you are not caught up to the anime series or manga!! (View by your own will)
Jellal Fernandes is the leader of the secret guild called Crime Sorciere. Jellal is an amazing wizard who has come by very tough obstacles in order to live the way he wants to live. Jellal was also a child slave from the Tower of Heaven and is where he met Erza. Jellal took the blame for one of his fellow slave friends and was tortured until he was also brain manipulated into a dark person causing him to become evil and work for the Tower of Heaven. Jellal even warned Erza that if he saw her still there in Tower of Heaven he would kill her. Jellal became a council member and one of the great wizard saints as well but all to hatch a plan to cause horrible destruction which of course was stopped by Fairy Tail's strongest team with the cost for Simons life(one of the child slaves). After that battle Jellal was thought to be dead until the dark guild Oracion Seis found his body and decided to bring him back to life so he could help them find a horrible magical weapon called Nirvana, with the help of Wendy's healing magic they brought Jellal back to life. Once Jellal was brought back to life he became pure again forgetting everything he had done in the past everyone he knew (except for Erza) and all the brain manipulation was gone as well causing Jellal great pain and confusion. Erza helps Jellal and he end up becoming a great help to the team and after they defeated the Oracion Seis Jellal is arrested for all his past crimes but before he goes he tells Erza that the reason he remembered her was by the color of her hair. After the 7 year gap Jellal along with two ladies (from the Grimoire Heart guild) Ultear and Meredy as a new guild that helps others in order to repent for their past crimes. Calling themselves Crime Sorciere. Jellal turning a new leaf in his life fights for what is right and helps to do what is possible so that he can at least do something after all the evil things he did. (and Erza lol CX)
Jellal uses Heavenly Body Magic. Jellal is able to use the four elements (Earth, Wind, Water and Fire) using his Abyss Break Spell. He was able to give Natsu some of the Flame of Rebuke to help defeat the leader of the Oracion Seis. Jellal is also able to use Telepathy and Telekinesis. Jellal can also mimic his Edolas counter part magic as shown to us in the Grand Magic Games. Jellal before was horrible and not one of my favorite characters bit along the way he changed into an amazing guy even First Master Mavis said that he has the pure kind heart like all the other Fairy Tail Characters which to me is more than enough reason to like him lol. Jellal is an amazing wizard no matter what side he was on.