'The Last of Us' made a major change to a game character. The showrunners explain why it was important to expand on Bill and his love story.

• Warning: There are spoilers ahead for season one, episode three of "The Last of Us."
• Sunday's episode expands greatly on a minor survivor from the video game, Bill (Nick Offerman).

Sunday's "The Last of Us" made a major change from the video game in the series' best episode yet, which is sure to be an early contender for one of the year's finest hours of television.

In a largely standalone episode, viewers were introduced to Bill (Nick Offerman), a doomsday planner who took over and safe-guarded himself in an abandoned Massachusetts town once the cordyceps infection took hold.

Over the course of 20 years, we watched his life in a series of intimate time jumps as he booby-trapped the town, fell in love with an outsider, Frank (Murray Bartlett), and lived out the rest of his days, growing old together while exploring his sexuality for the first time with his partner.

The pair's tender love story is a much richer and more respectful adaptation of Bill than the version that's glossed over in the game where his sexuality is merely implied, but never directly stated, and the relationship is depicted in a negative light.

In the game, Joel and Ellie seek out Bill, shown as a paranoid loner who speaks to himself, to help them fix up a vehicle and carry on across the country. Frank, also his partner in the game, is only seen dead, hanging after committing suicide some time ago after the infected bit him.

In the game, we learn the two had a nasty falling out, resulting in Frank's eventual death. In HBO's adaptation, the pair live out an idyllic existence, dying in each other's arms while never coming in contact with Ellie. Bill is still believed alive in the game.

During a Zoom conversation with showrunners Craig Mazin and Neil Druckmann, Insider asked why the show made these changes and expanded upon Bill's story in a significant way, giving him a happily ever after.

Mazin thought after two episodes filled with action and danger, there was an opportunity to take a breath in the story and change things up to show survival from a different vantage point.

"There's this lovely thread that indicated this hint of a relationship between Bill and Frank in the game," Mazin said, "I just suggested to Neil that maybe we pull that thread and we take it in a different direction in terms of the way it was depicted in the game, and use it to show the passage of time and use it to explore some of these themes that are so important to the length of the show, themes about what it means to love somebody, the different kinds of love, including a love that can be very protective and violent and dangerous, and how we could give these two men a win."

Mazin added: "They made it through. They had a long love and an ending that was actually quite peaceful and happy."

Druckmann added that Sunday's deviation from the source material allowed the series to do something the hit game couldn't.

Not only did it give us Bill's backstory, but it also gave us a slightly different, more optimistic version of Bill who we gradually see grow from a skeptical survivalist to a protective partner who has found something worth fighting for even at the world's end.

"In the game... mostly because we never leave Joel and Ellie's perspective, we can't see how Bill kind of lived his life," Druckmann said, adding that led to a conversation and exploration about what you "survive for" in an apocalypse. "When you do have a safe space, what is there left to live for?"

Druckman continued: "I love that Craig pitched this story of, 'Let's lean into that and just show it's a different Bill in that he's still — first is all about survival and nothing else. And here comes this other person that is still looking for the beauty in life, even in these horrific circumstances."

"This Bill, in this world — in the show's world — eventually changes and leans into that love and leans into, "Oh, this is what's important in this life," he added.

By the episode's end, Joel and Ellie arrive at Bill and Frank's house after they died. Bill has left behind a letter for Joel in which he passes on some advice.

The letter, in part, reads:

"...I respect you so I'm gonna tell you something because you're probably the only person who will understand. I used to hate the world and I was happy when everyone died. But I was wrong because there was one person worth saving. That's what I did. I saved him. Then, I protected him. That's why men like you and me are here. We have a job to do and God help any motherfuckers who stand in our way. I leave you all of my weapons and equipment. Use them to keep Tess safe."

Bill tells Joel to keep his partner, Tess, safe in the same way he protected Frank for years. Of course, Frank doesn't know that Tess recently died.

Druckmann told us the lesson Bill learned about "what's important in this life" on Sunday's episode reflects back to Joel and his current mission, given to him by Tess, to press on and believe in hope for the future by getting this girl, who could potentially be a cure to the cordyceps infection, out west.

Ellie's what matters. Ellie is who Joel must keep safe.

Of Bill's letter to Joel, Druckmann said, "He gives him this warning that's too late. Here's what you gotta do for Tess. And then Joel realizes, 'Well, it's too late for Tess. Maybe it's not too late for this kid.'"