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Dr. Jemma Simmons is a bio-chemist who works for S.H.I.E.L.D.. She was previously undercover in the terrorist organization HYDRA, tasked with providing Coulson and the rest of her team with key information. She specializes in life sciences (both human and alien) and is generally the partner of Agent Leo Fitz, an engineer.
Jemma is usually highly enthusiastic and has a bright personality. She has a deep passion for science. She is also very accepting and forgiving (examples include: forgiving Skye for betraying the team in "Girl in the Flower Dress"). Another one of her key traits is mercy (examples include not wanting to kill Centipede operatives in "The Magical Place".) Jemma can usually be found bickering with her best friend and partner, engineer Leo Fitz, and they are almost always found together. They are so close that Jemma and Fitz are often referred to as Fitz-Simmons, a gestalt entity. Despite Jemma's kind and calm nature, she cannot lie. When she tries to, she always ends up giving herself away, a bad habit. When pressured, she panics. She protested in the "Pilot" that she is "not Hermione", but, in "Seeds", Leo claims that she's so smart "because she loves homework more than life itself". Jemma loves her friends and always cares about their safe.
Jemma is a Caucasian female with light brown hair. She has brown eyes which sometimes looks hazel in different light, her height is about 5'4". She dresses a lot like Fitz by wearing flannel shirts, a lot of different style sweaters, ties, overcoats, and jeans.
Jemma is stated to be a genius bio-chemist. She is incredibly talented at her job that she graduated 3 years early and is becoming a star in S.H.I.E.L.D.'s research division. She has more than two PhDs.
A bio-chem genius with two PhDs, Jemma Simmons attended the S.H.I.E.L.D. training academy with her best friend, engineering genius Leo Fitz. Among their instructors were Professor Vaughn and Professor Hall, who taught chemical kinetics during their second year..
Wanting to see more than the inside of a lab, and against the advice of Professor Vaughn, Jemma convinced Leo to seek out a field assignment.
Jemma and Fitz were recruited by agent Phil Coulson to be the science crew for a new team he was putting together, although it has since been claimed by May that she was, in fact, responsible for their inclusion. Stationed on the Bus, the pair have designed specialized equipment and compounds on the fly in various emergency situations.
Their first foray into the field involved the case of Mike Peterson, a man in danger of exploding due to his use of the volatile Centipede formula. Peterson was saved in part by Jemma's efforts to create a Centipede counter-agent for Peterson. 
Jemma first faced danger in the field in Peru, where the team was investigating an 0-8-4. She and the team escaped Peruvian rebels only to face an armed takeover of the Bus. Working with the team, she helped take back the Bus and secure the old Hydra weapon.
While investigating a mysterious death in Pennsylvania, Jemma was infected with a fatal alien virus passed along from a Chitauri helmet. After what appeared to be a final failed attempt at a cure, Jemma threw herself from the Bus in flight in order save her team from the virus' effect. Fortunately for her, the cure was actually effective and teammate Grant Ward caught her in mid-flight, injected her with the antiserum, and parachuted them to safety.
When the team stopped at the Hub, Jemma and Fitz were forced to separate when Fitz and Grant went into the field. She was shown to fuss over Fitz a lot before he went, and made him a sandwich. Skye convinced Jemma to help her hack SHIELD, at great risk to Jemma's good-girl reputation. While accessing a wall panel, she was confronted by Sitwell, a superior officer. After many lame excuses and failed sweet talking, Jemma panicked and used the Night-Night Gun to shoot Sitwell in the chest. Coulson managed to get Jemma out of any serious trouble, luckily. The team rescued Fitz and Grant with perfect timing, and Fitzsimmons were very happy to be reunited. After Fitz bragged about how he had Grant's back, Jemma excitedly told him about how she had shot a superior officer in the chest, only to see his face fall.
At the beginning of "The Well", Jemma and the others are cleaning up after the events of the latest Thor movie. She ducks a call from her parents because she's been yet to tell them the events of "FZZT". A bit later, when the team goes to investigate a chopped down tree, Ward helps Jemma scale the tree, because she still has a fear of falling to certain death.
As of "Providence", Simmons appears to have the least faith of any of the original members in her colleagues, showing any real degree of trust only in Fitz.
In "Beginning of the End", Jemma found out that Fitz has loved her for a long time already, but she perceived him only as a friend.
In "Shadows" Coulson reveals that she has left the team, at least in part in the hope that forcing Fitz to recover without her will speed the process. It has, unfortunately, had the opposite effect, and her former partner is hallucinating her continuing presence. Despite appearing to have quit the team, she in fact was sent by Coulson to infiltrate HYDRA.
Season 2 Finale
In the end of the season 2 finale, Jemma was dragged into the strange object that the Inhumans were trying to secure. In the Season 3 Premiere, it was revealed that she had been transported to an alien planet. She was saved from the unknown planet by Fitz in "Purpose in the Machine ".
After a long, complicated search, Fitz was able to figure out how the portal works with the help of Daisy Johnson, Phillip Coulson, and other S.H.I.E.L.D agents. He tied a rope around himself and jumped through in attempt to save Jemma. Luckily Simmons was nearby and heard his voice, and he dragged her back through.
In the episode "4,722 Hours", the plot revolves solely around Jemma and her new friend Will Daniels, and reveals how she survived all of those long months on the planet without a sun. At first Will thought that she was evil, or a figment of his imagination, so he locked her up. Later however, he changed his mind and they developed a friendship and romantic interest with each other, and eventually found a pattern to when and where the portal back to Earth would be opening next.
In episode 8, Jemma and Leo are seen together researching how to rebuild the portal or make a device similar to the monolith that sucked Jemma to the other planet. In doing so, Jemma suddenly gets upset at Leo because he is being so helpful, and seemingly isn't mad that she fell in love with somebody else. Leo responds with saying that he is mad, just not at her. They then kiss for the first time in the series, causing Jemma to drop her book on the ground. When they break apart, she looks down at the book and realizes that the NASA symbol looks incredibly similar to the Hydra symbol upside down, which ties into Inhuman plot line that the other S.H.I.E.L.D. agents are working on with the ATCU during the same episode.
After 'starting over' their friendship in episode 11 of season three, Jemma and Leo, while trying to figure out how to cure Hive's parasite, kiss again in episode 17. At first, Fitz apologizes for moving too fast, bringing up Will and the fact that Jemma wished to start over. Jemma reassures him, saying that it's been 10 years and they can't waste any more time. They bring up Leo's comment that the cosmos are against them, and say that they won't let themselves be torn apart again. Leo states that he doesn't need space, as he has something magnificent right here. Simmons laughs and goes in to kiss him again, but he stops her to joke that he was talking about one of his most prized possessions, a poster of space. Laughing, Jemma interrupts him mid-sentence, kissing him once more. This implies that the best friends are now a couple.
Fitz: Colleague, research/work partner, best friend, love interest, boyfriend
Phillip Coulson: Colleague and team leader
Melinda May: Colleague
Mike Peterson: Former colleague
Trip: Former colleague and friend (deceased)
Bobbi: Colleague and friend (Disavowed)
Will Daniels: Former love interest and friend (deceased)
- Jemma - "jewel" in Italian, "little dove" in Hebrew.
- Simmons - patronymic surname derived from the ancient Hebrew Shimon, means "to hearken".
- Her current ID badge serial number is A 0956307; the card was issued on 5 February 2013, and will expire on 5 February 2018.
- As of "FZZT", both her parents are still alive. In a deleted scene from The Well, Jemma mentions being unable to help Ward or her parents due to their lack of knowledge about otherworldly biology, and there's no further explanation regarding why her parents would need help.
- As seen in "The Hub", her birthday is 11 September 1987. This is also the birthday of actress Elizabeth Henstridge, who portrays her. It is revealed she was Clearance Level 5.
- Fitz-Simmons named their eight flying gadgets after Snow White and Seven Dwarfs. 00 is Snow White, 01 is Doc, 02 is Sleepy, 03 is Grumpy, 04 is Bashful, 05 is Sneezy, 06 is Happy (07 hasn't yet appeared on screen). (0-8-4)
- While usually calm and collected, she's willing to lose her cool so that her point comes across. As seen when she asks Coulson to send the GH325's results to the Hub, so that they can understand it better and possibly help more people, and he forbids her. (Turn, Turn, Turn)
- It appears she's a fan of Harry Potter or is simply aware of its fiction. (Pilot)
- She apparently watches the British TV Show Doctor Who, as seen by her response in Providence when Koenig asks what's inside a box that washes up on a deserted island (She responds, "The TARDIS").
- For the majority of the series, Jemma only could see Fitz in a platonic way; however, she eventually confronts Fitz about what happened at the bottom of the ocean, implying that she may reciprocate his feelings for her which is confirmed in season 3.(S.O.S. Part Two)
Leo Fitz: The bullets work. Non-lethal, heavy stopping power, break up under the sub-cutaneous tissue-
Jemma Simmons: Oh, with a dose of .1 microliters of dendrotoxin. I'm not Hermione. I can't create instant paralysis with that.
Phil Coulson: We need a reset here, Fitz. Fitz? -
Jemma Simmons: Saying his name repeatedly does not increase productivity!
Jemma Simmons: Or maybe it does.
Jemma: [Imitating Ward] I'm Agent Grant Ward, and I could rupture your spleen with my left pinky... blindfolded. [Ward arrives]
Ward: Hustle up and grab your gear, we're on a mission... Is something funny?
Jemma: Poor silly Fitz, he mistakenly left a dummy round in the pistol. [Hands him the gun] Should be proper now.
Phil Coulson: Any idea what could cause an effect like this?
Jemma Simmons: There's the soliton hypothesis-
Leo Fitz: Well, okay, judging by the horizontal...
Jemma Simmons: Perhaps nanobatteries-
Leo Fitz: ...electrical discharge could be-
Phil Coulson: Time. Let's try again. Any idea what could cause an effect like this?
Jemma Simmons: Hell if I know.
Leo Fitz: Uh, no, no clue.
Phil Coulson: What's Fitz doing over there?
Jemma Simmons: He detected a strange energy coming off the body.
Phil Coulson: He's afraid of it, isn't he?
Leo Fitz: It's the smell.
Jemma Simmons: There's no shame in it, Fitz! It's perfectly natural to be afraid.
Leo Fitz: No, the only thing I'm afraid of is putrid decaying flesh corrupting my pristine workspace. (Jemma rolls her eyes) Do you remember the last time you brought a dead thing into the lab?
Jemma Simmons: Oh, not the stupid cat again.
Leo Fitz: The cat, tell him about the cat!
Jemma Simmons: And it's our lab Fitz, not your lab!
Leo Fitz: You left its liver next to my lunch!
Phil Coulson: Guys! Can we please...?
Skye: What if they're (Fitz and Ward) injured or being tortured somewhere right now?
Jemma Simmons: Fitz. Tortured. (pause) What exactly do you have in mind?
Leo Fitz: Enough mission talk already. Did anything exciting happen at the Hub?
Jemma Simmons: I shot a superior officer in the chest.
Leo Fitz: You screamed like a girl.
Jemma Simmons: I am a girl!
Grant Ward: That isn't a word in our language.
Jemma Simmons: Our language? You mean the English language, first spoken in England?
Jemma Simmons: Yeah, we couldn't have that, could we? It would be a shame if, especially if you're so, well, formed and symmetrical. Wh-when did you stop talking?
Leo Fitz: About three embarrassing sentences ago.
Simmons: I wish this bunker had a bunker.
Simmons: That's sweet. Though, apparently, I was miserable before I was born- upside down, umbilical cord all wrapped around my head.
Simmons: That means that every bit of energy inside us, every particle will go on to be a part of something else; maybe live as a dragonfish, a microbe, maybe burn in a supernova ten billion years from now. And every part of us now was once a part of some other thing - a moon, a storm cloud, a mammoth.-
Fitz: A monkey.
Simmons: A monkey. Thousands and thousands of other beautiful things that were just as terrified to die as we are. We gave them new life a good one, I hope.
Quotes about her
"FZZT" Coulson: There's only one person on this plane capable of finding a solution for this, and I'm willing to bet my life she will.
"Seeds" Fitz: Well, Simmons is probably smarter, technically, but that's only because she likes homework more than life itself.