Title: A (Pretty Little Liars)
Content:  "A" is a fictional character in the Pretty Little Liars franchise. Created by author Sara Shepard in 2006, the character serves as the main antagonist in both the television and book series. Working as an anonymous figure, “A” is a stalker who blackmails, manipulates and tortures the main characters of the franchise. In the novel series, the first and original "A" was revealed to be Mona Vanderwaal. The second "A" is revealed as Alison DiLaurentis and the third "A" as Nick Maxwell. In the television series, the first and original “A” was revealed to be Mona Vanderwaal. Mona later builds “The A-Team” with the help of the second “Big A,” Charlotte DiLaurentis. The series concluded with the third and final “Uber A” being revealed as Alex Drake, the twin sister of Spencer Hastings.
Title: Pretty Little Liars (season 3)
Content: Bianca Lawson as Maya St. Germain ; Missy Franklin as Herself ; Adam Lambert as Himself ; Amanda Schull as Meredith Sorenson ; Gregg Sulkin as Wesley Fitzgerald ; Téo Briones as Malcolm Cutler ; Aeriél Miranda as Shana Fring ; Brant Daugherty as Noel Kahn ; Steve Talley as Zack ; Larisa Oleynik as Maggie Cutler ; Bernard Curry as Jamie Doyle ; Jim Titus as Officer Barry Maple ; Annabeth Gish as Anne Sullivan ; Mary Page Keller as Dianne Fitzgerald ; Brandon W. Jones as Andrew Campbell ; Reggie Austin as Eddie Lamb ; Andrew Elvis Miller as Miles Corwin ; Nolan North as Peter Hastings ; Jim Abele as Kenneth DiLaurentis ; Robbie Amell as Eric Kahn ; Flynn Morrison as Malcolm ; Alexander Nifong as Sam 
Title: The DArkest Knight (Pretty Little Liars)
Content: Keegan Allen as Toby Cavanaugh, Spencer's ex-boyfriend and Rosewood P.D.'s officer ; Brant Daugherty as Noel Kahn, the Liars' long-time frenemy ; Lindsey Shaw as Paige McCullers, Emily's Ex-girlfriend ; Nicholas Gonzalez as Detective Marco Furey, the Rosewood P.D.'s head detective ; Rebecca Breeds as Nicole Gordon, Ezra's missing ex-girlfriend ; Kara Royster as Yvonne Phillips, Toby's wife ; Chloe Bridges as Sydney Driscoll, Jenna's friend ; Tammin Sursok as Jenna Marshall, one of the Liars' main rivals and a worker of "A.D." 
Title: Pretty Little Liars: The Perfectionists
Content: Sasha Pieterse as Alison DiLaurentis, a teaching assistant at Beacon Heights University (BHU). ; Janel Parrish as Mona Vanderwaal, the head of recruitment and admissions at BHU. ; Sofia Carson as Ava Jalali, a fashionable trendsetter with a talent for hacking and coding. ; Sydney Park as Caitlin Park-Lewis, the intelligent daughter of two overachieving mothers. ; Eli Brown as Dylan Walker, a talented cellist who is extremely critical of himself. ; Hayley Erin as Taylor Hotchkiss, Nolan's sister, who was a teacher at BHU before she faked her death. ; Graeme Thomas King as Jeremy Beckett, a charming and witty Brit and Caitlin's boyfriend. ; Kelly Rutherford as Claire Hotchkiss, Nolan's mother and founder of both BHU and Hotchkiss Technologies. 
Title: Sex, Lies and Alibis
Content:  Klea Scott was cast as a guest star in the episode as Dana Booker, BHU's new head of security. Scott previously recurred as Jillian Howe in parent series Pretty Little Liars.
Title: Pretty Little Liars
Content:  Pretty Little Liars is an American teen drama mystery thriller television series developed by I. Marlene King and is loosely based on the novel series of the same name written by Sara Shepard. The series follows the lives of five best friends whose clique falls apart after the disappearance of their leader Alison. One year later, the estranged friends Spencer, Hanna, Aria and Emily are reunited as they begin receiving messages from a mysterious figure named "A" who threatens to expose their deepest secrets. The series features an ensemble cast, headed by Troian Bellisario as Spencer Hastings, Lucy Hale as Aria Montgomery, Ashley Benson as Hanna Marin, Shay Mitchell as Emily Fields, Sasha Pieterse as Alison DiLaurentis and Janel Parrish as Mona Vanderwaal. The series premiered on June 8, 2010, on Freeform and ended on June 27, 2017. After an initial order of 10 episodes, ABC Family 
Title: The DArkest Knight (Pretty Little Liars)
Content: Troian Bellisario as Spencer Hastings ; Ashley Benson as Hanna Marin ; Tyler Blackburn as Caleb Rivers, Spencer and Hanna's love interest ; Lucy Hale as Aria Montgomery ; Ian Harding as Ezra Fitz, Aria's fiancée ; Shay Mitchell as Emily Fields ; Andrea Parker as Mary Drake, Alison's aunt ; Janel Parrish as Mona Vanderwaal, the Liars' long-time friend ; Sasha Pieterse as Alison DiLaurentis 
Title: Pretty Little Liars: The Perfectionists
Content: Chris Mason as Nolan Hotchkiss, a born leader and heir to the Hotchkiss empire. ; Duffy Epstein as Ray Hogadorn, an employee of BHU. ; Phillip Rhys as Michael Jalali, Ava's fugitive father. ; Cycerli Ash as Senator Park-Lewis, one of Caitlin's two mothers. 
Title: Pretty Little Liars (season 1)
Content: Troian Bellisario as Spencer Hastings ; Ashley Benson as Hanna Marin ; Holly Marie Combs as Ella Montgomery ; Lucy Hale as Aria Montgomery ; Ian Harding as Ezra Fitz ; Bianca Lawson as Maya St. Germain1 ; Laura Leighton as Ashley Marin ; Chad Lowe as Byron Montgomery ; Shay Mitchell as Emily Fields ; Nia Peeples as Pam Fields2 ; Sasha Pieterse as Alison DiLaurentis3 
Title: Pretty Little Liars
Content:  Hollywood Reporter also noted that Torrey DeVitto and Sasha Pieterse landed recurring roles in the pilot. The Alloy website later confirmed that Pieterse would be playing Alison DiLaurentis and DeVitto would be Melissa Hastings, also mentioning the casting of Janel Parrish as Mona Vanderwaal. In April 2010, the role of Aria's father Byron was recast with Chad Lowe, and Holly Marie Combs was cast as Aria's mother Ella. Jenna Marshall is played by Tammin Sursok. On January 13, 2011, Tilky Jones was cast as Logan Reed. On April 8, 2011, Annabeth Gish was cast for the role of Anne Sullivan, a 

Question: who is the head a in pretty little liars?
Answer: CeCe Drake.