A (Book Character)

A is an anonymous character (and the main antagonist of the series) who sends embarrassing and often threatening texts to Spencer Hastings, Aria Montgomery, Emily Fields, and Hanna Marin. There are three different A throughout the series. The first A is Mona Vanderwaal and the second A is Alison DiLaurentis. The identity of the third A (Helper A) is Nick Maxwell.

The First A
Three years after the disappearance of "Alison" DiLaurentis, her four friends, Aria Montgomery, Spencer Hastings, Emily Fields, and Hanna Marin, each receive message from someone calling themselves "A." The girls had drifted apart over the years, so they had no idea that other people were getting texts as well. Additionally, the texts were about secrets only Ali knew about. At first, the messages were simply teasing and all of the girls wonder if their missing friend was the one who sent them. Though they knew she was most likely dead, she was still the only one who knew their darkest secrets. Once Ali's body is discovered in her old backyard, the girls are even more baffled when they continue to receive threats. At Ali's funeral, the girls are reunited and they find out that they've all been receiving weird messages. As the girls stand outside after the funeral ends, they all get a text saying, "I'm still here, bitches. And I know everything.  — A"

From that point on, the messages take on a distinctly more threatening tone. Aria is given an ultimatum to tell her her mother about her father's affair by midnight after the Foxy event, or A will do it for her. A continues to play life-altering games with the girls, from encouraging suspicion of Spencer's involvement in Ali's death to outing Emily's sexuality to her conservative mother. However, A makes a serious mistake in texting Hanna on the night of Mona's birthday party. Instead of using the plain Blackberry she bought just for tormenting the girls, A accidentally uses his/her own phone. Hanna, who has a new phone without all of her contacts recognizes the number, compelling A to act before Hanna can reveal A's true identity to the others. A hits Hanna with an SUV, successfully destroying Hanna's phone and putting her into a coma that eventually leads to a temporary loss of memory.

A knew that there was a very good chance Hanna would regain her memory. Hanna's best friend, Mona Vanderwaal informs the girls that she has also received texts from A, drawing the five closer together in trying to figure who their tormentor is. Mona subtly encourages Spencer's fears that her sister, Melissa might be A as well as Ali's killer. During Hanna's recovery masquerade celebration, she suddenly regains her memory, revealing that Mona is A. However, she, Emily, and Aria can't do much about it, because Spencer and Mona are on their way to the police station. After Spencer is warned about Mona by text, she tries to escape Mona's car, but Mona catches on rather quickly and diverts to a path in a more remote area of Rosewood. She tells Spencer everything, from seeing Ali launch a firework into Toby Cavanaugh's treehouse and blind her friend Jenna, to finding Ali's diary of secrets among a pile of old DiLaurentis junk the St. Germains left at the curb, discovering the girls' secrets that only Ali knew. Her motivation was to get revenge for her friend's blindness, even though Jenna and Ali had planned together to launch the firework. Mona didn't know this and got a scar on her stomach from the ordeal. Mona also drops the bombshell that Ian Thomas killed Ali, due to Ali's last diary entry about giving him an ultimatum to break up with Melissa. She then offers Spencer to become A with her and tell Hanna that she must not be remembering correctly, but she refuses. The two fight at Floating Man's Quarry and Spencer accidentally pushes Mona, who falls and has her neck caught between rocks. She likely died instantly.

The Second "A"
As the girls move into the big red house they are shocked to receive messages from a new person claiming to be "A". At first, they believe it's just a prank, especially since the first "A" got major news time. Then the girls believe it's Ian Thomas, who is the prime suspect of the investigation. Spencer is especially certain of this until finding Ian's body in the woods bordering her estate and the old DiLaurentis home. The girls all get a message from "A," saying "He had to go. -A".

However, this "A" is even more twisted than the first; Ian's body disappears and the town is largely convinced that it was a hoax. "A" even teases Spencer, stating, "Just because I said Ian had to go, it didn't mean he had to die." "A" pretends to be Ian, using an IM screenname of USCMidfielderRoxx, a testament to his alma mater and his love for field hockey. Through this new fake identity, "A" feeds Spencer some interesting information about her family, specifically her father's affair with Mrs. DiLaurentis and the possibility that Ali is her half sister. "A" proceeds to torment the girls even more: they force Spencer to focus more on her father's secret by enabling Spencer's surrogate mother to scam her and clear out her two million dollar trust fund. "A" taunts Aria with pictures of her and her mother's new love interest in compromising situations. They threaten to send these to her mother, even though Aria has tried to ward off her mother's new boyfriend. "A" lands Hanna in the Preserve at Addison-Stevens, a lush clinic for troubled patients. "A" sends Emily on a trip to the Amish community in Lancaster to dig up more dirt on Officer Wilden.

Throughout the second half of the series, the second "A" keeps up this forced information search with the girls, pushing them to find more information on Wilden and Jason DiLaurentis. "A" even plants the idea that they killed Ali. However, when Jenna is found dead in "Heartless", "A" plants all of their texts, pictures, etc. on a random lecherous construction worker. This is one of the same workers who was involved in building the DiLaurentises' gazebo when "Ali" was still alive. The girls believe it is all over now, though the fact that the suspect is such a random person bothers them.

Everyone in Rosewood is shocked when the DiLaurentises introduce the existence of a third child, Courtney DiLaurentis. She is the twin of Alison and was kept in various clinics because she was "ill". However, "Courtney" is actually Alison DiLaurentis herself. She reveals her true identity to each of the girls, hoping to gain their friendship and telling them she never died the night of the sleepover. She claims that Courtney must have gotten out of the house and ran into the construction worker, who killed her. Though the girls believe her and are glad to have their friend back, Aria is the most suspicious of her. It was recently discovered that Courtney liked to pretend to be Ali and she wasn't completely buying her story. Additionally, Wilden and Melissa are also suspicious of "Courtney". Melissa knew about the twins since high school, as their brother Jason confided in her. He told her they hated each other, but Spencer tells her about "Courtney's" statements that she and Ali shared everything together."

Ali's time is running out, for besides the few people suspicious of her, the police start to say that the construction worker has an alibi and might not be guilty. Her secret is further endangered when Aria finds and sends in a photo of a reflection of someone spying on the girls during the sleepover. The reflection is too blurry, but it is clearly a female. Ali takes Mona's idea and convinces Spencer that Melissa is the culprit. Meanwhile, she kidnaps Melissa- who has just figured out the truth- and keeps her in her family's Poconos home. She stuffs Melissa in a closet with Ian's corpse.

On the night of the school's Valentine dance, Ali convinces the girls to hang out with her at the Poconos home. They ditch the party and get wasted at her home. She asks them if she could reenact the night of the sleepover and hypnotize them. Everyone reluctantly agrees, and minutes later they wake up to find Ali gone and the door of the room locked. A letter is slid underneath, informing the girls of the horrible truth: The Alison that they had been friends with had been Courtney all along and the real Ali killed her.

Courtney was mentally unsound and wanted to be Ali so badly that she tried to drown her when they were children. One day, when she was home from the mental institute, Courtney stole Ali's ring and imitated her when she saw Spencer and the others sneaking into their backyard. Ali was sent to the new mental institute, the Preserve, in Courtney's place, and was forced to take her sister's messed up life. On the night of the sleepover, she spied on the girls, followed Courtney after her fight with Spencer, and killed her in revenge for taking her perfect life. She hates the girls for ruining her life and tries to kill them too by boarding up the entire home and setting it on fire. The girls, including Melissa, manage to escape, but no one knows whether Ali is alive. It's hinted that she might be, as Emily hears a faint giggle in the distance as she visits Courtney's grave in the evening.

The Third "A"
The third "A" seems to be Ali, as Emily desperately wants it to be. She torments them about the Jamaica Incident, Spencer's framing of Kelsey of drug dealing, Emily's baby, and Hanna framing Madison for the car crash. Later, A admits to killing Tabitha, and guess what? They're next. This new "A" seems to be more violent; so far, four people (Tabitha, Gayle, Kyla, and Graham) have been killed, and numerous more injured, under this "A"'s tenure.

By the end of "Crushed", the Liars know that the Second "A", Alison, has had an accomplice the whole time, and that this accomplice is the Third "A". They believe that Alison did indeed survive the fire in the Poconos house, and thus that the Second and Third "A" are currently operating together to bring them down (and eventually kill them).

The Third "A" also knows as the Helper "A" is revealed to be Nick Maxwell.

Murder

 * Courtney DiLaurentis ("Ali's Pretty Little Lies"): Second "A", with help from Third "A".
 * Ian Thomas (Discovered in "Wicked", confirmed in "Wanted"): Second and/or Third "A"
 * Jenna Cavanaugh ("Heartless"): Second and/or Third "A"
 * Tabitha Clark (Discovered in "Twisted", confirmed in "Deadly"): Second and Third "A".
 * Gayle Riggs ("Stunning"): Third "A"
 * Kyla Kennedy ("Crushed"): Most likely Third "A"
 * Graham Pratt ("Crushed"): Most likely Third "A"
 * Greg Messner ("Toxic"): Second "A"

Serious Injury/Attempted Murder
 * Hanna Marin ("Perfect"): First "A"--hit her with a car (which almost killed her, left her in a coma, and gave her partial amnesia)
 * Spencer Hastings ("Unbelievable"): First "A"--tried to strangle her, tried to shove her off of Floating Man's Quarry
 * The Liars ("Killer"): Second "A"--tried to kill them in a fire in the woods behind the Hastings' house
 * Melissa Hastings ("Wanted"): Second "A"--knocked her out, kidnapped her, locked her in a closet with Ian's corpse
 * The Liars and Melissa ("Wanted"): Second "A"--tried to kill them by locking them in the Poconos house and burning it down
 * Madison Zeigler (Occurred between "Wanted" and "Twisted"; revealed in "Burned"): Second and/or Third "A"--hit Madison's car (which Hanna was driving), knocking Madison out and leaving her badly injured
 * The Liars ("Burned"): Second and/or Third "A"--tried to kill them by destroying their lifeboat, leaving them to drown
 * Noel Kahn ("Crushed"): Second/Third "A"--severely beat him, leaving him unconscious. It is later revealed in "Deadly" that Noel survives.

Memorable Quotes
These are the first messages the girls received from the first "A":

Spencer (after flirting with her sister's boyfriend): Spencer, covet is an easy one. When someone covets something, they desire and lust after it. Usually something they can't have. You've always had that problem though, haven't you? -A

Aria (after finding out her romantic interest is her new AP English teacher): Aria, surprise! I wonder what your pig puppet will have to say about this...-A

Emily (after kissing the new girl): Hey Em, sob! I've been replaced! You've found another friend to kiss! -A

Hanna (after getting caught for shoplifting): Hey Hanna, since prison food makes you fat, you know what Sean's gonna say? Not it! -A

Mona's botched message to Hanna: "Oops! Guess it wasn't lipo! Don't believe everything you hear! -A"

Aria, Emily, Spencer after hitting Hanna with a car: "She knew too much. -A"

The second A's memorable quotes:

Honestly, bitches...did you really think I'd let you off that easy? You haven't gotten nearly what you deserve. And I can't wait to give it to you. Mwah! -A

(About Emily after the girls tell the police about New A): You all told, and one of you has to pay the price. Wanna know where your old BFF is? Look out the back window. It just might be the last time you see her...-A

(After the girls discover Ian's body in the woods): He had to go -A