Pein is actually 6 seperate bodies, connected by their eye, the legendary Rinnegan which was only possessed by the founder of the ninja world. In fact, the true possesor of the Rinnegan has not yet been seen in person in the current time, as Nagato presumably resides in safety while manipulating his puppets through using the Rinnegan. Having developed a God complex. Pein believes he alone understands pain and suffering, and wishes to end it by monopolizing war and destroying all the great ninja villges.
Pein's abilities are incredibly powerful and fascinating. All 6 of the bodies share vision, a huge advantage during combat, while Rinnegan allows the Deva Path, the main Pein body to use almost any technique. Other bodies can absorb attacks, summon great beasts, revive and heal the bodies...but the most powerful ability comes from the main body, an ability called Shinra Tensei. It allows Pein to control gravity in small or large proportions, reflecting any force sent at him or creating a huge gravity well capable of obliterating entire villages.
Pein...don't wanna fuck with him.
SHINRA TENSEI! *toads get knocked back waaaay the hell out there*
"I am Pein...I AM GOD!!!"