This character is known by different names depending on the translator. Jellal is a direct romanization, while Gerard is an alternative that completes sounds the Japanese language can't phonetically produce.
Jellal is initially introduced under the alias Siegrain, a young member of the Magic Council and the main antagonist of the series. His design mirrors that of Sieg Hart from Rave Master, Hiro Mashima's previous work, as a nod to fans. Alongside his "underling" Ultear, he often disagrees with the rest of the Council, typically showing leniency towards Fairy Tail.
Though it's revealed early in the series that he has a history with Erza, the nature of their relationship isn't clarified until much later. As a child, Jellal was forced to help build the Tower of Paradise. While there, he was possessed by what he believed was Dark Mage Zeref, replacing his kind personality with a more violent one. He helped Erza escape, took control of the Tower’s construction, and worked his way into the Magic Council as "Siegrain."
Eight years later, Jellal had Erza kidnapped to be used as a sacrifice to revive Zeref. He convinces the Magic Council to destroy the tower to fuel the resurrection system. After fulfilling their purpose, he destroys the Magic Council and tries to execute his plans. Erza confronts him but is defeated; Simon, another childhood friend, is killed. Jellal is stopped by Natsu, who uses the magic powering the system against him. Before the Tower self-destructs, Jellal regains his senses and helps Erza escape. Ultear reveals she had been manipulating Jellal all along, and his attempt to revive Zeref was futile since Zeref was never dead.
Jellal uses "Heavenly" magic, allowing him to move and fly at meteor-like speeds and create black holes. Though supposedly killed after fighting Natsu, he was recently revived by Sky Dragon Slayer Wendy. Upon revival, he only remembered the name Erza. He found Nirvana and released its seal to destroy it. Regaining his former self, he's horrified by his past actions. Initially, he casts a self-destruct spell to free Erza from her anger. She convinces him to live, and he helps them destroy Nirvana. He remembers Natsu and provides flame to defeat Zero, master of Oracion Seis.
At the battle's end, Jellal admits fearing memory recovery, but Erza promises support. Before she can elaborate, the new Magic Council arrives and arrests him for treason. As he's taken away, he recalls naming Erza after her hair color.
Jellal can also be in multiple places simultaneously due to a powerful thought projection spell. He played as Siegrain at the council while being at the Tower of Paradise simultaneously. Mystogan, revealed to have the same face, is later shown to be the Edolas version of Jellal.
Seven years later, many Fairy Tail members return from their disastrous S-class mage test, revealing Jellal escaped prison. With Ultear and Meredy, he formed "Crime Sorcière" to repent for their sins, meeting Team Natsu while investigating a suspicious magical force. Jellal privately talks to Erza, leading to her slapping him before they almost kiss. Embarrassed, Jellal lies about having a fiancée, prompting comments on his poor lying skills from Ultear, Meredy, and Erza.
During the Grand Magic Games, Jellal disguises himself as Mystogan and competes with Fairy Tail Team B to investigate the earlier suspicious magical force.
