The Dragon Ball franchise is home to all sorts of powerful beings. From the Saiyans to the Namekians to the godly Kais, there are plenty of powerful opponents to choose from for anyone itching for a fight. Yet some characters out there are implied to be powerful, but have had very few opportunities to show it. A prime example of this is the Grand Kai.
In Dragon Ball, the Kais are gods assigned to watch over a certain quadrant of the universe. For example, the classic King Kai is specifically the North Kai. Sitting above the four quadrants' Kais, however, is the Grand Kai. He doesn't watch over any particular part of the universe, but ensures the other Kais are doing their jobs properly and provides advice when necessary. But if Grand Kai watches over those who protect the universe, then he has to be pretty strong, right?
Unfortunately the Grand Kai has never really had a chance to shine, due to -- by his own admission -- neglecting his own training. He even bent the rules of a tournament he hosted so he wouldn't have to make good on his promise to train Goku. While he's never been shown actually fighting, it's implied he's weaker than Goku in his Super Saiyan form.
While that might sound pretty underwhelming for someone who's supposed to be a god watching over other gods, there are still hidden bits of info that imply the Grand Kai is stronger than he lets on.
While the Grand Kai doesn't have much to show in the way of actual fighting, he's given glimpses of his power before. At one point, Goku and the East Kai decide to race each other, and though he wasn't a part of the competition, the Grand Kai decides to join in for the fun of it. Despite Goku and the East Kai both having a head start, the Grand Kai races ahead of them with absolutely no issue, reaching the finish line long before the other two even come close.
On the opposite side of the coin, the Grand Kai had trouble keeping up with Goku and Pikkon during their fight at the Other World Tournament finale. He weaseled his way out of training them because he wasn't confident he could teach them anything that would make them more powerful than they already were.
Despite this, the Grand Kai didn't immediately assume he was outmatched. Rather, he assumed that while Goku was more powerful than him now, he could reach the Super Saiyan's power level by taking his training seriously for once. Whether or not he actually followed through on that idea is yet to be seen.
The Grand Kai is definitely more powerful than the Kais who serve under him. Whether he's more powerful than the Supreme Kais, or any other fighter capable of going toe to toe with them, is up for heavy debate. One thing's for sure, though -- while he may not look the part, the Grand Kai is still definitely not someone you want to mess with.