It seems to me people become check airmen for one of two reasons:
1. They truly care about their coworkers and truly want to make sure everybody operates in the safest and most efficient manner.
2. They get off on any and all versions of power, real or imagined.
Fortunately, most checkies at my airline are very much the former, but there are a few (a few sim instructors as well) who fit the latter profile way too well.