The Quintessence is a group of all-powerful beings who kept tabs on the order of the universe. It's members are the Olympian God Zeus, the New God Highfather, Phantom Stranger, the wizard Shazam, and Ganthet, one of the guardians of the universe.
The group was first seen in the alternate future Kingdom Come series. It was later introduced into normal continuity. However, with the deaths of Shazam in Day of Vengeance and Highfather in Death of the New Gods, it is unclear if the group disbanded, or if their heirs took their places in the group.
The Quintessence reappeared in 2018's Justice League #1. Ganthet, Highfather, the Wizard and the Phantom Stranger were still part of the group. After Zeus was killed by Darkseid, his wife Hera assumed his place in the Quintessence. They pushed the Justice League forward with the energy of Dr. Manhattan to fight against Perpetua.
The group attempted to bring Wonder Woman into their ranks but she refused. They were then slaughtered by Darkseid, who they thought defeated.