#9 Roman Reigns
Roman Reigns completed the Grand Slam after he triumphed over The Miz to win the Intercontinental Championship on the 20th of November, 2017.
Before that, Reigns was a WWE Tag Team Champion with Seth Rollins in 2012. He won the US Title in 2016, and the WWE Championship the year prior to 2015.
Reigns has been pegged to be the next Cena (someone who is yet to complete the Grand Slam) and hasn't been well received by the crowds.
However, that hasn't stopped him from rampaging through the main roster up until 2016. After 2016, he has been shown to be more human, losing to Finn Balor, Rollins and taking the pinfall in the Shield Triple Threat that same year.
He had a strong 2017, being prepped for Lesnar at WrestleMania 34, but was dominated and put to rest easily.
Reigns has had consistently strong booking, but WWE have been using him incorrectly, which isn't endearing him any further to the WWE Universe.
However, when the boos can be looked past, Reigns has been a dominant force, who has won everything and dominated everyone.
This consistency put him up there with some of the greats in WWE.