As a group, they have played 401 games together, including the playoffs. They have watched each other suffer serious injury. They have watched each other struggle and they have been there for each other both on and off the court.
Now, the group will face their ultimate test.
Garnett is 35 and is on his last legs. This could be the last season for the decorated veteran. How sweet it would be to end it with a title.
No one is giving the Celtics much of a chance this year, though.
The Celtics are too old. The Celtics rely on too many injury-prone guys. The Celtics have been past their prime since Garnett went down in 2009.
What will the Core Four do?
Will they fight Father Time and make one final push for that second NBA Title, or will they roll over and die?
With Kevin Garnett on the team, you know there is only one answer: this team will fight to the death.
Here are five reasons why the Celtics' Core Four can make one more championship push this (hopefully) upcoming NBA season.