MIAMI -- For just the second time since Dan Marino retired, the Miami Dolphins have signed a quarterback to a multiyear extension.

Tua Tagovailoa agreed to a four-year, $212.4 million deal with the Dolphins that includes $167 million guaranteed, sources confirmed to ESPN's Adam Schefter. It's the richest contract in franchise history, and the guaranteed money is the eighth most among NFL quarterbacks.

It also ends a two-day standoff between Tagovailoa and the team, in which he was a minimal participant in Miami's practices at training camp.

Tagovailoa joins Ryan Tannehill as the only quarterbacks to re-sign with Miami since Marino retired after the 1999 season. Tagovailoa, selected fifth overall by the Dolphins in 2020, is also the fourth quarterback from the 2020 class to sign an extension with the team that drafted him, joining Joe Burrow, Justin Herbert and Jalen Hurts.

"We're strong believers in him. And you guys all feel [coach Mike McDaniel's] passion about him when he talks about him," Dolphins general manager Chris Grier said in February. "Just in the two years of what he's done, he's grown in areas to where he led the league in passing and did some great things this year. And we all feel there's still another level he can take it.

"The way he's attacked this and wants to be great, and the combination of Mike and working with that and that trust and belief in each other, we do think there's still another level which he could go."

The Dolphins have publicly supported Tagovailoa over the past two years under McDaniel but offered their largest display of faith to date by giving the new deal.

Here's how both sides got to this point.

Why did the Dolphins make a commitment to Tagovailoa?

Tagovailoa was unremarkable during his first two NFL seasons, completing 66.7% of his passes for 4,467 yards and 22 touchdowns against 15 interceptions in 2020 and 2021.

He has blossomed under McDaniel while completing 67.4% of his passes. The former Alabama player led the NFL in passing yards in 2023 with a career-high 4,624, playing a full season for the first time in his career (more on that later).

His draft classmates got off to stronger starts to their careers, but Tagovailoa's first two years in Miami were marked by a lack of continuity. The Dolphins cycled through three offensive coordinators and two quarterbacks coaches in those first two seasons before hiring McDaniel in February 2022.

Since McDaniel's arrival, Tagovailoa has thrown for the fourth-most passing yards (8,172) and fifth-most touchdowns (54) in the NFL. Tagovailoa's 102.9 passer rating and 67.4% completion percentage also rank second and fifth in the league, respectively.

The Dolphins have started 25 different quarterbacks since Marino retired at the turn of the century, but Miami believes Tagovailoa is its franchise cornerstone and has rewarded him as such.

Is there any risk in the long-term deal?

Entering the 2023 season, there was considerable skepticism regarding Tagovailoa's ability to stay healthy for an entire season -- skepticism he met by changing his offseason preparation.

Tagovailoa bulked up to 225 pounds and trained in a jiu-jitsu break-fall course to learn how to keep his head from hitting the ground as it did on three notable occasions in 2022. It worked, and he finished the 2023 season without any major injuries.

But while Tagovailoa has thrived inside the structure McDaniel has built, he has struggled to create when plays broke down. He ranked third in quarterback rating when he attempted a pass in under 2.5 seconds (78.9). Beyond 2.5 seconds, he dropped to 16th (43.2).

His off-target throw percentage doubled on passes that took longer than 2.5 seconds to throw, from 11.2% to 22.1%. Considering his concussion history, teams don't fear him as a runner; he picked up five first downs on the ground in 2023, which ranked 41st among qualified quarterbacks.

Tagovailoa's accuracy and anticipation are his trademark strengths. His playmaking ability falls short of some of his peers, such as Lamar Jackson, Josh Allen and Patrick Mahomes, but the Dolphins are banking on his strengths outweighing his weaknesses moving forward.

What took so long?

The negotiations left Tagovailoa feeling "antsy" as he watched the Detroit Lions sign quarterback Jared Goff to a four-year, $212 million deal with $170 million guaranteed.

The feeling didn't subside after the Jacksonville Jaguars inked Trevor Lawrence to a five-year, $275 million extension with up to $200 million in guaranteed money.

Tagovailoa was absent for a portion of the team's offseason program before mandatory minicamp -- which he attended, in full -- and kept an eye on how quarterback deals were getting managed this offseason.

"I'm not blind to people that are in my position who are getting paid," he said. "Am I concerned about it? I'm not concerned about it, but there's a lot of discussion that we've had. We're just trying to move that thing in the right direction to where everyone can be happy."

The guaranteed money -- which ended up being $167 million -- in Tagovailoa's deal might have been a point of contention through the negotiating process, a front office source told ESPN in May. Tagovailoa's durability concerns were prevalent entering the 2023 season, but he played all 18 games for the Dolphins last season and seemingly debunked said concerns.

What does this mean for the Dolphins' Super Bowl window?

It's still open, but it's time to capitalize.

Miami now has premier offensive players signed for the foreseeable future in Tagovailoa, wide receivers Jaylen Waddle and Tyreek Hill, and running back De'Von Achane. The NFL's top-ranked offense last season also added veteran wide receiver Odell Beckham Jr. as well as rookie wideouts Malik Washington and Tahj Washington.

With a couple of tweaks and some good health, Miami's offensive line is good enough to give its playmakers time to make an impact.

Defensively, the Dolphins have several young core players under team control, plus a star veteran in Jalen Ramsey. But the clock is ticking. Eventually, those budding stars will need contracts, and Tagovailoa's deal will ultimately hinder Miami's ability to bring everyone back on deals considered to be at market value.

The AFC features a gauntlet of talented quarterbacks Miami must get through to reach its first Super Bowl since 1984. It believes that, with Tagovailoa under center, it has enough to do exactly that.