Al Horford has been indispensable for the Celtics. It’s time for him to win his first NBA title.

I’ll spare you the whole replay, as the main dividing line, Kyrie Irving, now stands between the Celtics and their first title since 2008, and the Kyrie: The Boston years storyline gets new life.

Let’s briefly return to that Horford vignette from the immediate aftermath of the end of that 2018-19 Celtics season, a roster implosion that would soon follow the one on the court in a five-game semifinal loss the conference against the Bucks. (It should be noted that Milwaukee didn’t even have Jrue Holiday yet. Irving and the Celtics were cooked by George Hill.)

The Celtics locker room and overall atmosphere after that loss was as weird and disturbing as any I’ve seen. While Irving gave a monologue on stage about his future (“I just want to get to Boston first, you know, safely…”), the Celtics left in the locker room played on their phones and ignored each other.

It was Horford who finally stood up, cut through the awkwardness and indifference, and spoke with his usual thoughtfulness to a swarm of reporters about the ugly ending, and what might happen next.

Horford was asked about an opt-out in his contract that he was entitled to. He said he hoped to stay with the Celtics. Two months later, after reports that a mystery team was interested in his services, he signed a four-year contract worth $109 million… with the rival 76ers. Ouch.

When Horford, who in July 2016 became the first major league free agent to ever sign with the Celtics, left for Philadelphia, it was devastating. Losing the erratic Irving, who stopped playing for the Celtics in that Bucks series long before he officially stopped playing for the Celtics, was one thing.

But the loss of Horford, the ultimate teammate? It meant that what Danny Ainge and Brad Stevens were building had collapsed on itself, and the implications of that bedeviled those who remained. Were Jayson Tatum and Jaylen Brown really the cornerstones of the franchise? Were they copacetic? How long would it take before the Celtics were real contenders again?

The Celtics survived that catastrophic offseason better than anyone expected, in large part because Tatum and Brown, as hardworking as they were talented, continued their march toward all-league status. The Celtics made it to the conference finals the first season without Horford, who didn’t suit up for Philly — an indictment on that organization if ever there was one — and was soon banished to Oklahoma City for what would ultimately be a postponement.

When Stevens, in his first trade since taking over as president of basketball operations after the 2020-21 season, reacquired Horford from the Thunder for creaking knee pad Kemba Walker, it felt like a wrong had been righted.

Horford is a quintessential Celtic – versatile and unselfish, proud and feisty when challenged (see: Giannis Antetokounmpo, floor-bound, Game 4 of the 2022 conference semifinals). I will always believe that the misery of the final weeks of that ’18-’19 season – along with 109 million other reasons – drove him to Philly. But in terms of style and spirit, he has always belonged here.

Reacquiring Horford was one of many Auerbachian moves Stevens has made in assembling the best team in the NBA. (The Derrick White deal has to be his best, right? Although I hear you on Jrue Holiday, who will be the difference in the finale, you’ll see.)

Horford turns 38 on Monday, three days before the Celtics begin the most challenging phase of this championship mission. He’s a young man in life, but not by professional basketball standards, and it’s always funny to watch a “This weather?” look flashes across his face before he answers another question about his age with his usual thoughtfulness.

Horford is in a strange place historically. He has played 181 playoff games, including seven as a rookie in the Hawks’ first-round battle with the eventual champion Celtics in 2008. Trailing only the Jazz’s pick-and-roll tandem of Karl Malone (193) and John Stockton ( 182) played more without winning a championship.

Should the Celtics win, Horford would be the 10th oldest player to win a championship. (Current Celtics assistant coach Sam Cassell won with the ’08 Celtics at age 38; Robert Parish is the oldest to do so, collecting a ring as a 43-year-old bystander for the Bulls from 1996-97 .)

Al Horford is averaging 9.9 points, 7.3 rebounds and 1.9 assists in the playoffs.Danielle Parhizkaran/Globe Staff

No one should need a reminder that Horford is still essential. The Celtics are 9-1 in the absence of Kristaps Porzingis this playoff round, in part because Horford stepped into the starting lineup without skipping a beat. No one really considers him a bench player anyway; he looks more like the sixth starter.

Should the Celtics beat the Mavericks in the Finals, Horford will be the person everyone is second most happy with, right after themselves of course.

He remains one of the easiest Celtics to like, conscientious and effective as ever, even at his advanced basketball age. (Somehow he just felt that I wrote that and frowned.)

But we all know this, and hopefully he knows it too. There aren’t many gifts Horford could receive on his 38th birthday that equal in value to the gifts the Celtics received when he returned to Boston.

Chad Finn can be reached at [email protected]. follow him @GlobeChadFinn.