In the manga, Beryl was a beautiful girl on Earth during the age of the Silver Millennium. She was in love with Prince Endymion, but her love was unrequited; when she discovered Endymion with Princess Serenity of the moon, she was crushed. She later states that having Endymion was her sole reason for siding with the evil force from the sun, Queen Metaria. She was corrupted and empowered by Metaria, and used her new powers to mobilize the Earth in a war against their protectors, the Moon Kingdom. Beryl killed Prince Endymion as he was trying to protect Princess Serenity, leading to the princess's own suicide. At some point after this, Sailor Venus killed Beryl with the holy moon sword. Queen Serenity, greatly weakened, sealed away Metaria again, and before dying sent the whole of her Kingdom to be reincarnated on Earth. Beryl is stated to be "reborn" when the Senshi meet her again in the 20th century. She became Queen of the Dark Kingdom, communicating with Queen Metaria and wielding her reincarnated generals Jadeite, Nephrite, Zoisite, and Kunzite to find the Silver Crystal and defeat the newly-awakened Sailor Soldiers. In the end she fails to get the Silver Crystal, and is again killed by Sailor Venus, who drives a sword through her body. As she falls, she says Endymion's name, and murmurs that she had always just been watching him.
In the anime, Queen Beryl is the mastermind behind the various attacks against the citizens of Tokyo while Sailor Moon, and later the other Sailor Soldiers, are searching for the Moon Princess. She also kidnaps and brainwashes Prince Endymion in order to force him to kill his lover. But when he breaks free of her control and attacks her she lies in a swoon and begs Queen Metaria for more power, which results in Beryl becoming Metaria's vessel for the destruction of everything on Earth. Queen Beryl is soon vaporised along with Metaria when Sailor Moon, who has transformed into Princess Serenity, combines the power of the Silver Crystal with that of the Moon Stick.
She is generally portrayed in a more tragic light in the manga than she is in the anime, even experiencing a brief moment of regret as she knows that she can no longer turn back.
In the English-dubbed anime no mention is given to her origin and she is only said to be the ruler of the Negaverse, an evil alternate dimension, from which she was somehow able to escape in order to attack this dimension. At the end of the season Beryl is said to be merely banished back to the Negaverse when Sailor Moon defeats her.