Queen Beryl is the first enemy in Sailor Moon. Before the series, her minions attacked the Moon Kingdom. In order to defeat Beryl and her forces, Queen Serenity seals her and her forces away using the silver crystal. Beryl’s seal was broken at some point in the future, around the time that the the Sailor Senshi were resurrected on Earth, also thanks to the silver crystal. She had four generals, all of whom used to be loyal to Earth’s prince, Endymion, who in the present day was brainwashed into aiding Beryl.
While it is unknown if Beryl will be in the new anime, it’s very likely. Here is an epic scene from Pretty Guardian Sailor Moon, where Queen Beryl is fighting Sailor Moon.