4: Kevin Owens
Last year was an interesting one for Kevin Owens. He and Roman fought in an amazing No disqualification match at the Rumble, then he dropped the Universal Championship in disgusting fashion, and went on to turn on his best friend. He was also involved in two of the ten longest matches of the year. The Smack Down Money in the Bank ladder match and his Hell in a Cell match with Shane O'Mac. Also in 2016 Kevin Owens defended the intercontinental championship at a house show in an iron man match versus AJ Styles.
He may not have the stereotypical build of a Vince McMahon top guy. That is exactly what he is though. He has put in some of the most grueling and gut wrenching match ups WWE has had over the past five years. That is why he is one of WWE's iron men.