In the first season of "The Last of Us," Joel faces a difficult decision when he learns that the Fireflies plan to operate on Ellie's brain to find a cure for the cordyceps virus. Despite the potential for a cure, Joel chooses to save Ellie by killing the doctors and lying to her about the situation. In season 2, a five-year time jump reveals a strained relationship between Joel and Ellie, culminating in Joel's brutal death at the hands of Abby, seeking revenge for her father's death. The show explores the moral complexities of Joel's actions and the consequences of his choices.
Source: https://www.slashfilm.com/1867120/the-last-of-us-creator-fireflies-cure