Lydia, Scott, and Stiles knew each other for years though Lydia paid no attention to either Scott or Stiles as she was in a relationship with the jock Jackson Whittemore and she pretended to be ditzy and unintelligent for his benefit.
After being bitten by Peter in Season 1, Scott became a Werewolf and along with Stiles, ended up having more interaction with Lydia who would go on to become one of the earliest members of the pack along with Allison. In the first two seasons, their interactions were limited, partially due to her past relationship with Jackson. Their friendship fully blossomed in Season 3A after Jackson left for London and Lydia began to learn more about her powers and aided them in finding out who is sacrificing innocent people.
This trio is also known as Scilydia or McMartinski by fans.
Throughout Teen Wolf
In Wolf Moon, Stiles and Scott are seen talking about the dead body Scott found in the woods. Stiles mentions that the discovery is the best thing that happened since the birth of Lydia Martin, who coincidentally is walking past them. Stiles tries to greet her, but she merely walks past them, ignoring them. Stiles then proceeds to blame Scott for bringing him down to his "nerd depths", as Lydia barely acknowledges their existence.
- They have known each other since the third grade.
- Lydia caused a small rift between Scott and Stiles by kissing Scott in Lunatic.
- In Galvanize, Scott and Stiles help Lydia learn to use her Banshee wail to drown out all the voices in her head and help her hear what she needs to.
- They are the only original pack members/characters that are present/alive throughout the entire series.