Ellie - The Last of Us
Among the cast of The Last of Us, I felt that Ellie was the strongest person. Despite her young age, she has already seen and experienced extreme hardships in a hostile and confusing world.
Ellie grows along her journey with Joel, learning about the world that existed not too long before she was born while fortifying her personal strength and courage by facing the dangers wrought by the fungal pandemic.
She learns what it means to be a human being while many people she encounters have long forgotten. She learns how to protect but also the meaning of sacrifice. By the end of the game, the player develops a bond with Ellie that is extremely uncommon in any kind of storytelling I've seen.