#4 Sheamus
Sheamus and Roman Reigns are no strangers to each other. Both of them were involved in a lengthy feud for the WWE Championship back in 2015. It started when Roman Reigns was scheduled to face Seth Rollins for the WWE Championship at Survivor Series 2015, but Rollins suffered a knee injury at a live event, which forced him to vacate the title.
A WWE Championship tournament took place, which Reigns won by defeating his Shield brother Dean Ambrose in the final round. Moments later, Sheamus cashed in his Money In The Bank contract on Reigns to become a four-time WWE Champion. However, Reigns was able to recapture the WWE Championship the following month by defeating Sheamus on an episode of RAW.
Sheamus then formed a Tag Team with Cesaro, which was known as The Bar. The Bar had a decent run, but Sheamus and Cesaro parted ways after The Celtic Warrior was forced out of action due to spinal stenosis. Sheamus made his return to SmackDown earlier this year in January, where he took out Shorty G. Upon his return, Sheamus expressed his displeasure at the state of SmackDown, and put the locker room on notice.
Since Reigns and Sheamus are both on the Blue brand, it is only a matter of time till the two former rivals cross paths again.