Sherri Mackleberry

Sherri Mackleberry is the sister of Terri, and is the eldest of the twins by two seconds. She is in the same class as Bart at Springfield Elementary School.

Biography
The twins are quite bright students (they even have their own language) and are often very conniving and mean, even to each other. When it comes to Bart they are quite stuck up, and never miss an opportunity to berate him. They fed Bart intentionally false information on American history, however both girls correctly guessed that Bart had not prepared himself for a test and was looking to get all the answers from a student who studied, so the prank was arguably to teach Bart a lesson in slacking; since if he had studied he would have realized the information was false.

Principal Skinner apparently considers Sherri smarter or more talented than Terri, because in Simpson Tide he announces, "In the event of nuclear war, we can only save our best, and brightest. Therefore, space in the fallout shelter will be reserved for: Lisa Simpson, Martin Prince, our championship kickball team, and Sherri, but not Terri."

Bart appears to have a crush on one of them. Sherri (or possibly Terri) referred to Bart as an ugly, smelly dork, but was convinced by Homer to go on a date with Bart after he told her that neither she nor Bart could do much better. One of the twins stated that her sister had a crush on Bart it is unknown if this is the truth or if it is just teasing. She also has a "boy crazy" cousin who has a crush on Bart.

When it comes to Lisa they are just as inconsistent. One minute they will be friends on the schoolyard playing together and the next they will be ganging up on her. More often than not it is the latter, usually not including Lisa because she is too smart or too weird. Once they said her butt was too fat causing Lisa to go on a diet.

In the Simpsons and Family Guy Crossover episode Sherri is pushed by a kid into Terri causing Otto to hit them with his schoolbus.

Future
Professor Frink shows Bart and Lisa a possible future with his astrology machine. It is revealed that Nelson simultaneously dated and impregnated both Sherri and her sister, who bore him four children (two sets of twins, naturally) shortly before Nelson's high school graduation. He abandoned them during Bart's graduation party, using the same statement his father said to him before abandoning him.

The Simpsons Arcade game
Sherri and Terri appear in stage 1 and 2 carrying a burger in a plate for the Simpsons to gain their health.

Mob Rules
Sherri and Terri appear with an Itchy mask and act as enemies that must be defeated.

Big Super Happy Fun Fun Game
Sherri and Terri also appear as one of the holders of the three Sparklemon that Homer and Lisa must defeat.

Behind the Laughter
Creation​ They have similarities to the Grady Twins (ghost girls) Danny sees in Stanley Kubrick's adaptation The Shining, of Stephen King's novel of the same name. In a deleted scene of the parody of the Shining called "Treehouse of Horror V" they are ghost twins seen by Bart. They also take on this role in The Simpsons Game; they are in a game engine el​evator saying "Come play with us, Simpsons".

Trivia

 * Matt Groening said Sherri is always on the left in an episode commentary.
 * Both she and Terri bear some resemblance to the twins Patty and Selma, as both hold an enjoyment for tormenting the males of the Simpson family, but for different reasons, and have a close relative who have a romantic crush on one of the Simpsons.
 * It is implied that Sherri and Terri are not actually twins, but two thirds of conjoined triplets, although this is conjectural, and should be considered non-canon until said 'sister' officially appears.
 * She apparently doesn't like Arby's restaurants, and would only eat there if she were starving.
 * Sherri and Terri's last name was finally revealed in the new episode Yellow Subterfuge, written on Principal Skinner's list of students.