No brainer to me.
Pierce was the Captain but KG was the straw that stirred the drink. Locally, the '01-02 run put the Celtics back on the map for a lot of Boston sports fans after a dreadful decade but it was the KG acquisition that really kick-started the Celtics resurgence in the region. The impact of his arrival in town was huge. Then when the games actually started in '07-08, it was like "Whoa". He definitely changed the culture inside that locker room and pulled back in the casual Celtics fans. His importance on the court was glaring.
In today's day & age of sports, its rare that you're going to see guys play 10-15 years with one organization. Guys move around. KG might've only been in Boston for 6 seasons but with his accomplishments during that time on the court and with the impact he made, I have zero qualms with having his number being retired. The Celtics have retired numbers for guys who've done lesser.
I’ll never forget opening night in 2007. Every season opener is exciting for a variety of reasons, but I cannot remember a season that comes remotely close to 2007 (2008 was next for the repeat and 2017 was actually up there too, but we all know that excitement lasted less than 6 minutes).
Obviously we had a lot of hype (and our fair share of doubters), but watching KG go nuts for the first time against Washington was amazing. We blew them out easily and Garnett showcased his talent (monster 20/20 game and was everywhere on defense) and the new culture of the Boston Celtics.
Also a little sad reminiscing because that injury in 2009 was truly heartbreaking for him and the team, as I think they may have been even better that season than 2008 and clear title favorites. There’s valid reasoning to think a healthy Garnett may have spearheaded a true dynasty (three-peat?) for the ages.
Nonetheless, I was always in awe of the dedication to his craft and couldn’t be happier that his number is going into the rafters alongside #34.