Pre-Crisis

Before Crisis on Infitite Earths, the Emerald Empress was Sarya of Venegar.

In the middle of the 30th Century, Sarya discovered the legendary Emerald Eye of the lost Ekron civilization on her native planet of Vengar. She used the eye's almost limitless power for a variety of evil purposes and at one point conquered the planet Vengar.

Joining together with a group of the galaxy's worst villains summoned by the Legion of Super Heroes to defeat the menace of the Sun Eater, she became a founding member of the Fatal Five. She worked with her fellow members on several occasions, but also continued her solo career in an attempt to dominate her own planet or any other she took a shine to.

Emerald Empress went on to create her own version of the Fatal Five when Tharok and Validus were unavailable. She recruited her former teammate, Persuader, and recruited three new members: Flare, Caress and Mentalla. 

Emerald Empress eventually revealed to her respected nemesis, Sensor Girl, that the Emerald Eye actually held her captive, and not the other way around, and wanted nothing but to die. Sensor Girl granted her that final gift and used her ability to 'blind' the Emerald Eye, allowing Sarya to die in peace.

Post Crisis

The Emerald Empress appearing in Legionnaires is known as Cera Kesh.

Post Zero Hour

The most recent Emerald Empress simply went by the name of Empress. In the present, Lobo has been seen with the Emerald Eye during the course of 52, so Empress is presumably either depowered or dead. She has recently battled Batman and Blue Beetle(Jaime Reyes).

In other media
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She appears in JLU battleing the Legion of Superheroes.