Lydia Martin, is a smart, popular, and beautiful student at Beacon Hills High School on the MTV series Teen Wolf.
She is also a Banshee.
Lydia is portrayed by Holland Roden.
Lydia has developed quite a bit since she met Allison Argent, Scott McCall, and Stiles Stilinski.
She was, on the surface at least, shallow and spoiled but this turned out to be an elaborate act to hide the fact that she possesses a genius level IQ. She is well versed in chemistry and understands both classical and archaic Latin.
The ruse, along with her relationship with Jackson Whittemore, was part of a carefully orchestrated plan to maintain her popularity at Beacon Hills High School.
Lydia was manipulative with her friends, using them whenever it suited her ambitions.
As the supernatural elements began to close in though, her carefully crafted façade began to fall apart. After being attacked at the winter formal by Peter Hale, she found herself haunted by her attacker. She was later able to show her true love for Jackson and it was that love which saved his life.
Jackson's abrupt move to London, England seemed to leave Lydia emotionally numb. She returned to her "just on the surface" existence and took a number of lovers over the summer, expressing a "love them and leave them" philosophy.
When supernatural threats arose again, Lydia found herself drawn to gruesome murder scenes again and again. She learned she was a Banshee and decided to use her abilities for the greater good... if she can figure out how to actually use her abilities.
She fell in love again too. While she had entered into a purely physical relationship with Aiden to aid her friends in defeating the The Alpha Pack, she developed deeper feelings. She once again suffered genuine heartbreak when Aiden was killed.
Although her feelings may not be as strong for Stiles, they have developed a strong and caring friendship.
Lydia is one of the few characters for which we have an firmly established age.
In Omega, Sheriff Stilinski reports Lydia is a "16-year-old" she then celebrates a birthday a few weeks later inParty Guessed making her 17.
In Season 4, Natalie Martin alluded to Lydia's upcoming 18th birthday as "a few weeks" away. It apparently passed off screen.
In Season 5, Lydia is confirmed to be 18 by Deputy Parrish.