#2 Brock Lesnar
Brock Lesnar has been booked as an unstoppable force ever since his WWE debut in 2002. In around five months after making his arrival on the main roster, Lesnar won the WWE Championship. Shortly after, he feuded with the likes of The Undertaker, Big Show, Kurt Angle, and John cena among others before walking out of the company in 2004.
During his first WWE stint, Lesnar was once involved in a feud with John Cena, but it lasted for only a month as they had a legitimate beef between them. Owing to Cena's sudden rise in WWE, Lesnar found it very hard to work with him and it's been reported that he bad-mouthed Cena to Vince McMahon every time he tried to do something positive.
While it seemed as if Brock Lesnar and John Cena buried the hatchet after the former parted ways with WWE in 2004, that wasn't the case at all. As you already know, Lesnar fought Cena at Extreme Rules 2012, and it was his first match in WWE in over eight years. Even though Lesnar dominated most of the bout, he was defeated by Cena in the end.
Reportedly after the match, John Cena was supposed to be carried out on a stretcher to show how dominant The Beast Incarnate was as an opponent. However, Cena decided to cut a promo after his victory and walked to the gorilla on his own feet. As you can imagine, Lesnar lost his cool in the backstage area and blamed many people including Cena for trying to ruin his career.