Red Coat

Big A is an unknown character, responsable for the creation of "A" and the A- Team. Little information is known about this person, and only makes appearences wearing a red trench coat. Big A is considered to be the true A and the leader of the A- Team, as he/she is the one calling the shots, and telling his/her workers (aka minor A's) what to do (such as ordering Mona to hit Hanna with a car, ordering Toby to steal Alison's body and ordering the deaths of Ian Thomas and Garret Reynolds). Though this characeter is considred to be the main A, he/she has little to no physical  involvment with the Liars since he/she orders his/her team members to actually do the things that A has been known to do to the liars.

We have only seen Big A twice. The first time is at the end of the season two finale, unmAsked, where he/she visits Mona after being revealed as an A- team member. Big A is seen wearing a red trench coat. Mona looks up to Big  A, and says: "I did everything you've asked me to." From this point, it becomes clear that he/she is the leader of the A- Team. The second time is at the end of the season 3 episode of "Blood is the New Black", where he/she is seen buying black hoodies and gloves for his/her workers. Again, he/she is seen wearing a red hoodie. The store owner says to Big A: "So, are you buying this for a team?".

It is possible that Mona was talking to Big A in "The Lady Killer", as it was clearly shown that Mona was taking orders from someone when she said: "I understand" on the phone.

It is possible that Big A makes his/her workers physically do the things that A does to the liars because he/she does not want their identity to be traced back incase the Liars discover a new -A team member, or so called "minor A". While the A- team members are known to wear a black hoodie, black gloves and black pants, Big A makes their appearence in a red trench coat or a red hoodie.