Pretty Little Liars is the first instalment of the Pretty Little Liars universe and the series from which Pretty Little Liars: The Perfectionists is spun-off. The series was developed by I. Marlene King and ran seven seasons from 2010-2017.
Set in the small suburban town of Rosewood, Pennsylvania, the series follows the lives of girls: Spencer Hastings, Aria Montgomery, Hanna Marin and Emily Fields, whose clique falls apart after the leader of the group, Alison DiLaurentis, goes missing. One year later, the remaining estranged friends are reunited as they begin receiving messages from a mysterious villain named "A", who threatens and tortures them for the mistakes they have made before and after Alison was alive. At first, they think it is Alison herself, but after her body is found, the girls realize that someone else is planning on ruining their lives. Eventually the Liars discover that Mona Vanderwaal, best friend to Hanna, is "A". Mona is set to Radley Sanitarium for treatment and joins forces with a partner, known as Red Coat. Mona and Red Coat torment the Liars, with help from a team of stalkers known as the A-Team. Eventually it is discovered that the identity of Red Coat belongs to three people: Alison DiLaurentis, who is alive and on the run from the A-Team, CeCe Drake, who is the leader of the A-Team and Alison's cousin/adoptive sister, and Sara Harvey, who is a decoy hired by Drake. Alison and the Liars are finally at peace until CeCe is murdered, prompting the rise of a new Uber "A", going by the title "A.D.", and working with an updated A-Team, consisting of Jenna, Sydney, Aria, Wren, Mary, and Mona. Uber A recruits Original A, Mona, in the series finale to assist her in the endgame. Uber A is revealed to be Spencer's twin sister, Alex Drake, who wanted revenge for CeCe's murder. The series ends with Alison living happily engaged with Emily and their two and Mona kidnapping Alex and her mother Mary Drake.
- 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. Germain
- Laura Leighton as Ashley Marin
- Chad Lowe as Byron Montgomery
- Shay Mitchell as Emily Fields
- Nia Peeples as Pam Fields
- Sasha Pieterse as Alison DiLaurentis
- Tyler Blackburn as Caleb Rivers
- Janel Parrish as Mona Vanderwaal
- Andrea Parker as Jessica DiLaurentis/Mary Drake
- It is currently unclear how much of the storyline from this series will be referenced in Pretty Little Liars: The Perfectionists, other than Alison DiLaurentis and Mona Vanderwaal.
- The storyline of Mona kidnapping Alex and Mary Drake will possibly receive attention in Pretty Little Liars: The Perfectionists.