Once a noble doctor, Dr. Jekyll creates a serum that seperates the good self from the bad self. He uses his other half, Mr. Hyde, to blackmail Arthur Lydgate into accepting him in the prestigious academy Jekyll desires, and also tries to get Hyde to convince Lydgate's daughter Mary to fall in love with Jekyll. However, when Jekyll learns that Mary has fallen for Hyde instead, he becomes livid and ends up killing Mary in his blind rage. Afterwards, he and Hyde are sent to the Land of Untold Stories by Rumplestiltskin.
In the Land of Untold Stories, Jekyll meets Snow, David, Hook and Zelena, who are all trapped in the realm. Jekyll aids the group, and after being physically separated from Hyde, goes with them to Storybrooke.
With Jekyll's technology, Hyde is imprisoned in an asylum beneath Storybrooke Hospital. When Snow, David and the other heroes require Jekyll's help again, this time to defeat the Evil Queen, Jekyll requests a suitable laboratory. He is then subsequently introduced to Dr. Frankenstein, who allows Jekyll to use his scientific equipment. However, when the lab is destroyed by Hyde and Jekyll's work is stolen by Rumplestiltskin who wants to take matters into his own hands, Jekyll seeks revenge on Rumplestiltskin's wife Belle. While attempting to harm Belle and her unborn son, Hook intervenes and kicks Jekyll over. Jekyll lands on a spear which impales him through the back, killing him and also killing Hyde. This reveals the Evil Queen will only die if Regina dies.
- Mr. Hyde (bad self)
- He is based on Dr. Henry Jekyll from the story The Strange Case of Dr. Jekyll and Mr. Hyde.
- S5, E22: "Only You"
- S5, E23: "An Untold Story"
- S6, E01: "The Savior"
- S6, E03: "The Other Shoe"
- S6, E04: "Strange Case"