Jefferson was once a portal-jumper, who owned a magical hat which allowed him to cross to realms, but only realms with magic. He worked for Rumplestiltskin, who sent Jefferson to Oz to obtain a pair of slippers that would allow Rumplestiltskin to travel to a land without magic, but he fails and instead he gives Rumplestiltskin a crystal ball which he begrudgingly accepts. Jefferson introduces Regina to Viktor Frankenstein, who is testing a new procedure which could bring the dead back to life with the help of hearts that have been magically ripped out. Jefferson retires from portal-jumping after a confrontation with the March Hare results in the death of his wife.
Jefferson has a daughter named Grace and they live a life of poverty but happiness. One day, Regina visits Jefferson and asks him to help her cross another realm, but he claims to have given up portal-jumping because it had something to do with the death of his wife. However, Regina says that Grace will want for nothing if he accepts, and so he brings the hat to Regina's castle. Regina and Jefferson travel to Wonderland where Regina rescues her father, who had been kidnapped by the Queen of Hearts. However, Regina and her father abandon Jefferson and escape back to the Enchanted Forest, leaving him behind. Jefferson is brought before the Queen of Hearts, who has him executed. However, Jefferson's head is somehow still alive, and he is ordered to make an exact magical replica of the hat before having his head returned to his body. Jefferson is kept prisoner, where he makes thousands and thousands of hats, but none of them work and Jefferson begins to go mad.
While Emma Swan is looking for Mary Margaret Blanchard, she nearly runs over Jefferson. She stops the car and sees that Jefferson is wounded from dodging the car, so she drives him back to his house. Emma goes inside, and Jefferson makes her a cup of tea. However, Emma realizes that the tea is drugged and falls unconscious after discovering that Jefferson was faking his limp. Emma wakes up and finds out Jefferson has Mary Margaret too. Jefferson orders Emma to make a magical replica of his hat, claiming that since Emma is the savior then she should be able to get it to work. Jefferson still has the memories of his past life, despite being under the Dark Curse. Emma and Mary Margaret escape after Mary Margaret kicks Jefferson out of the window, but he quickly runs off before they can see him. Regina gets Jefferson's help when she requires her poisoned apple from the Enchanted Forest to put Emma under the Sleeping Curse. Jefferson uses the small amount of magic in some of Regina's belongings to activate his hat and obtain the poisoned apple. However, Regina does not keep her end of the bargain - making Grace remember who she is - so Jefferson frees Belle from the asylum and tells her to go to a man called Mr. Gold and tell him how it was Regina who locked up Belle in the first place.
After the first Dark Curse is broken, Jefferson is trapped in an overturned car after the wraith attack but is rescued by David Nolan. David questions Jefferson about the magical hat, but Jefferson is no help at all and escapes. He later reunites with his daughter Grace.
Once Upon a Time in Wonderland
The Mad Hatter is not seen, but he is mentioned by the White Rabbit who says the Hatter has not been in Wonderland for a long time. Will says that Jefferson is currently living in Storybrooke where Will was living. They also travel to the Mad Hatter's house in an attempt to find Cyrus. Will also uses the phrase, "Mad as the Hatter".
- He is based off the Mad Hatter from Alice's Adventures in Wonderland and Through the Looking-Glass.
- Jefferson has been to Wonderland, Oz and the Land Without Color along with presumably many other realms. However, he has a hatred towards Wonderland even before his imprisonment there.
- His name, Jefferson, is a reference to the band Jefferson Airplane. This is probably because of their song "White Rabbit". His daughter Grace is named after the lead singer of the band, Grace Slick.
- S1, E17: "Hat Trick"
- S1, E21: "An Apple Red as Blood"
- S1, E22: "A Land Without Magic"
- S2, E02: "We Are Both"
- S2, E03: "Lady of the Lake"
- S2, E05: "The Doctor" (flashback)
- Bk 1: "Reawakened"
- Bk 3: "Out Of The Past" - Tea Party In March