The In-Betweener works in the shadows, between problems, trying to find solutions.
The only time you will realize all that they do, is when they are not there, where issues and problems begin to arise at an increasing rate.
They keep the tensions low, they keep things from simmering over and they always keep their eye on the prize.
The In-Betweener is the person on your team you never interviewed for but are glad they joined your team.