Ever since Dragon Ball, Goku and the Z Fighters have met omnipotent beings wielding the power of the gods, with escalating strength. Dragon Ball Super opened with Goku and Vegeta fighting Beerus, their universe's God of Destruction, who -- along with his constant companion Whis -- was the strongest deity they had encountered at that time. Halfway through Dragon Ball Super, however, the characters encountered Grand Zeno, a supreme being that oversees the entire Dragon Ball Multiverse.
Here is a quick overview of Zeno and whether he truly is the most powerful being introduced in the entire Dragon Ball mythos.
Grand Zeno
Grand Zeno is introduced at the end of the Tournament of Destruction, pitting the best martial artists of Universes 6 and 7 against each other in a friendly competition. Appearing following Universe 7's victory, Zeno is initially annoyed that he hadn't been invited to the proceedings by the Gods of Destruction serving under him but this was tempered by his enjoyment of watching the fighting contest from afar. The Gods of Destruction are seen to be in clear fear of Zeno's vast destructive potential and cower in respect.
According to Whis, Zeno reigns over the Dragon Ball Multiverse as its Omni King and had erased six entire universes when he found himself in "an unpleasant mood." Prior this unseen event, there had been eighteen universes within the Multiverse, now, only twelve remain. Quickly befriending Goku, Zeno makes him promise to meet him in his home outside of the twelve realities to have fun on a playdate, befitting his childlike appearance.
Future Zeno
Following the Tournament of Destruction, Goku and the Z Fighters accompany the adult Trunks from his alternate future timeline where they face the rogue, rampaging demigod Zamasu, who has possessed the body of Goku from a parallel world. Initially, Goku and Vegeta are able to overpower the villain after fusing themselves into the composite Saiyan warrior Gogeta and utilizing the Super Saiyan Blue transformation before the fusion wears off and Zamasu grows more monstrously powerful.
As Zamasu begins to spread across the entire timeline's reality, Goku summons this timeline's Zeno who does not recognize him, revealing that each timeline's reality has its own presiding Omni King, suggesting that Zeno does not exist outside of time. Witnessing Zamasu's spread, Zeno erases all of this reality, with Goku and the others barely escaping in Trunks' time machine. Deciding to give his timeline's Zeno a playmate, Goku and Trunks later return to the erased timeline where they find the alternate future Zeno as the only thing remaining and introduce the Omni Kings to one another, with the omnipotent pair becoming fast friends.
The Omni Kings
The Omni Kings invite the remaining universes to the Tournament of Power, a battle royale between the twelve universes, pitting teams of their greatest warriors against one another. To increase the stakes, the Zeno threaten to erase any universe that is eliminated from the competition. This is steadily made true as the Zeno erase entire universes with the casual wave of a single figure. In the end, the Zeno allow Android 17 to restore the Multiverse with the Super Dragon Balls, announcing that they had foreseen a selfless champion winning the contest and restoring the Multiverse.
The level of awareness and power demonstrated by the Zeno is completely unseen. Kami, the first godly figure seen in Dragon Ball couldn't even defeat Piccolo at the end of the original series while King Kai, the god seen at the start of Dragon Ball Z, was ultimately killed by Cell. Even the Supreme Kai acknowledged that Goku was stronger than him in his Super Saiyan form, conceding to the protagonist when they reached a disagreement. While Beerus has displayed strength outclassing Goku, nothing has the sheer power of the Grand Zeno from either timeline, has been seen. Zeno can completely obliterate an entire reality without any visible degree of visible exertion and appears to be aware of much around him. Commanding the deepest respect from Beerus, Zeno is the most powerful being in the Dragon Ball mythos to date.