Quarantine Question of the Day: Who are the five toughest Celtics in team history?

Unfortunately we will have no recaps or Green Envy's for a while, so figured it might be fun and give people a distraction to debate in the comment section on a different question every day while we are stuck in this new normal.

Today's question:

Who are the five toughest Celtics in team history?

Old-timers are going to have an easier time with this than younger folks, so I'm curious to read their answers. By "tough" it can mean whatever you think the word means. An enforcer? A guy who rarely ever missed games? A great defender? You get the idea. Anyway rank them from 5 to 1 with #1 being the toughest guy to ever wear Celtics green.