Does Ryan Merriman play A in Pretty Little Liars?

Answer 1

No, the real A's (yup, plural!) are Mona Vanderwaal & Alison.

Up until book 4 Mona is A, she stole Alison's diary (well actually it's Ali's twinsister Courtney's diary, but I'll explain that later on) so she knows all the secrets.

However, in book 4 she dies whilest trying to push Spencer off a cliff. Bam, dead.

Allison has had an identical twinsister no one knew about, cuz she's mentally ill (courtney is ill, not ali). Their parents wanted to send Courtney to a clinic but acidentally sent Ali.

Courtney pretended to be Ali & wrote all the girls' secrets in her diary, which Mona found after the real Alison escaped from the clinic & buried courtney alive (YIKES!)

Mona finds the diary & becomes A.

After Mona's death, the real Alison becomes A.

Hope you understood..?