- “Awesome. He resisted, we can shoot him.”
- —Tammy's last words before her death.
Tammy Guterman was a deep-cover agent for the Galactic Federation, and the supposed daughter of Pat Gueterman and Donna Gueterman. She was also a student at Harry Herpson High School and a close friend of Summer Smith. She was engaged to Birdperson and planned a wedding as a ploy to gather as many enemies of the Galactic Federation in one location in order to capture and arrest them. After the fall of the Federation, she became the leader of the remains. However, she was killed afterwards by Rick when attempting to hunt down Space Beth. She is the secondary antagonist of Rick And Morty.
Tammy made her first appearance in the episode "Meeseeks and Destroy", where she made a brief cameo in the audience during Mr. Meeseek's assembly about the benefits of a friendship with Summer and can be seen gathering around her afterwards. She makes another cameo appearance in "Rick Potion No. 9", and later became a Cronenberg. An alternate version of Tammy appeared again and had her first major role in the episode "Ricksy Business" at Rick and Summer's party. After seeing Brad arrive at the party she asks her friend to mess up her hair so she looks drunk. Tammy, however, starts talking to Birdperson who is apprehensive about Tammy's overt desires. When Birdperson tells Tammy that he is not looking for a soul-bond Tammy responds by whispering something in his ear to which he replies "I believe Birdperson can arrange that." Ultimately, Tammy goes home with Birdperson at the end of the party.
She later appears in the episode, "Get Schwifty" in Birdperson's home, casually dressed in a robe, implying their relationship has continued and making a sly innuendo that Birdperson and Morty found highly uncomfortable. She is later seen watching the transmission of the events back on Earth with horror.
In "The Wedding Squanchers", Tammy reveals during her wedding reception speech that she is a deep-cover agent for the Galactic Federation. After declaring that everyone at the reception is under arrest she shoots a confused Birdperson several times in the torso with a laser rifle after he ignores her order to sit down. In the ensuing shoot-out, she exchanges fire with Rick and is last seen falling over with Squanchy stepping on her foot.
Tammy's parents were the Guetermans, Pat and Donna. They briefly engage in conversation with the Smiths Jerry and Beth before the ceremony,and are later revealed to be cyborgs, likely as part of Tammy's cover. They pursue the Smith family, and immediately after boarding their getaway vehicle, they both fall off the back of it while it's in mid-air.
In "The Rickshank Rickdemption", Tammy is revealed to have survived the shoot-out in "The Wedding Squanchers" and is now the leader of its remaining party. It is also revealed that the Galactic Federation has revived Birdperson, now renamed "Phoenixperson", although Tammy wanted him to be called Cyber Bird.
Tammy returns in Star Mort Rickturn of the Jerri, where she was pursuing Space Beth who was running an escapade across space. Tammy tracks Beth and Jerry to the office of their therapist Dr. Wong and doesn't believe Beth's story of being a clone after she shows her activities in space. However, Rick saves Beth and Jerry, due to rigging the office and escaping Tammy. Tammy finds Beth in the streets with her double and sees that there are really two versions of Beth. Regardless, she arrests both and tries to ignore Rick because he is second fiddle to Beth now. When he resists, she orders her men to shoot him but Summer and Morty appear and kill them. Rick then overpowers and executes Tammy for making him go to her sham wedding and killing his best friend. Her corpse is used to infiltrate her base. When Phoenixperson learns of Tammy's fate, he attacks Rick and nearly kills him along with the two versions of Beth. However, Jerry distracts him with Tammy's corpse, allowing Beth to shut off Phoenixperson.
Tammy is a teenage white girl with medium dark brown hair. She wears a blue sweater that exposes her midriff and khaki pants. She may not really be the age she claimed to suit her undercover character.
In "The Wedding Squanchers", she wore a short, white wedding dress, heels, flowers, and a pinecone as her wedding ring from Birdperson.
In "The Rickshank Rickdemption", she wore a bright, shiny, red and black leather suit, with an upturned collar, and silver shoulder pads with the Galactic Federation symbol on its sides.
Tammy appeared to be a flirty and sarcastic girl with a craving to be popular at school. Her biggest problem was that she doesn't have a boyfriend and she feels like she needs to act cool in front of them by doing immoral things such as drinking and watching abnormal kinds of pornography. She was very boy crazy, overall and some of the porn she watches, such as bukkake, interests that part of her. When she started dating Birdperson, she appeared happy and secure with her life, but she was still very sex-crazed around him and didn't care to keep those feelings private when other people were around.
However, her actual personality could be described as cold-hearted, cunning, cruel, insecure, yonic, determined, two-faced, selfish, power-hungry and callous.
In the episode "The Wedding Squanchers", it was revealed that her entire personality was fake and that she was just an undercover agent from the Galactic Federation who put on a fake schoolgirl guise for a period of time, in order to catch Rick Sanchez, and other intergalactic terrorists meaning almost all of this was fake. She is actually cunning, manipulative, Machiavellian, and loyal to her cause.
It is possible that the only feelings that she had that weren't entirely fake were that for her husband, as she revived him as Phoenixperson.
Despite Rick having single-handedly destroyed the Federation, Tammy did not try to get revenge on him as she knew that Rick would remain a "non-threat" as long as he was left alone and because Beth was a greater priority. However, she did try to attack him, once he resisted her order but was overpowered by his grandchildren. In the end, her arrogance led to her death, as Rick promptly executed her for killing his friend and going to her wedding.
- She likes watching Bukkake, but she doesn't know if she would ever do it. This may not be true and just be part of her act as a high school student. 
- She goes through three different tones of voice. Her first was the voice of a regular teenage girl. After meeting Birdperson, she started talking in a seductive, sexual voice. And then after revealing herself to be a member of Galactic Federation, she talked in a very strong-willed and stern, but professional, voice.
- Tammy Guetermann (C-137) was almost certainly also working for the Galactic Federation in Dimension C-137 and most likely died along with the rest of humanity unrelated to Morty.
- She knows that Rick can go to live in other dimensions, as she suggested he do so in their confrontation.
- Her last name is borrowed from writer/producer Dan Guterman.