Paul Pierce officially signed a contract with the Boston Celtics on Monday, a formality that brings his 19-year NBA career full circle, back to the team with which it began in 1998.

The contract will allow Pierce, who played 15 seasons in Boston and helped bring the city an NBA championship in 2008, to retire as a Celtic.

“It’s an honor to have this opportunity to once again call myself a Boston Celtic,” Pierce said in the team’s press release. “The organization and city took me in and made me one of their own, and I couldn’t imagine ending my career any other way. I’m a Celtic for life.”

A Celtic for life, indeed. Pierce’s No. 34 will undoubtedly hang from the TD Garden rafters before long. And he will almost surely have a place alongside other Celtic greats in Springfield, Massachusetts, when he becomes eligible for the Hall of Fame.

Pierce played 1,102 games during his 15-year career as a Celtic. Those 15 years rank second in longevity in franchise history, trailing only John Havlicek’s 16. He made 10 All-Star teams, won 14 playoff series, reached two NBA Finals and won one Larry O’Brien trophy.

Pierce tops the team’s all-time leaderboards in 3-point field goals, free throws and steals. He currently sits third in games played, minutes played (40,360) and field goals made (7,882); fourth in blocks (668); fifth in assists (4,305); and seventh in rebounds (6,651).

Most importantly, Pierce helped bring Boston its only NBA title of the past 30 years. After he and an insufficient supporting cast missed the playoffs twice in a row in 2005-06 and 2006-07, general manager Danny Ainge traded for both Ray Allen and Kevin Garnett, who, along with Pierce, formed Boston’s Big Three. The Big Three won the title in their first season together.

Nine years later, the members of the 2008 championship team still share a close bond — except for one. Ray Allen hopped to Miami in 2012 to win another ring, and in doing so complicated the legacy he left behind in Boston. His departure prompted Garnett and other ’08 Celtics to leave Allen off reunion guest lists, and it’s likely the reason behind the franchise’s decision to give new free agent signing Gordon Hayward the No. 20, meaning Allen’s No. 20 almost certainly won’t be retired.

But in a way, the team’s awkward relationship with Allen further underscores why Pierce is so beloved in Boston. The Celtics — players and fans — questioned Allen’s loyalty. Pierce, on the other hand, was loyal to the Celtics for an entire decade before the title, and remained loyal afterward. That’s why he’ll be a legend in Boston.

That’s why he’s a Celtic for life.

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