The Empress is the (current) most powerful royal caste xenomorph present. A hive develops an Empress through first creating 2 Daughter Queens. As soon as one of the Daughter Queens produce their first Daughter Queen, the original queen becomes an Empress.

Summarized Development.

Queen. - Two Daughter Queens - Daughter Queens establish Hive. - Daughter Queen has their own Daughter Queen. - Original Queen molts into an Empress.

Daughter Queens travel far away from hives before establishing their own hives. However, unlike a “Solo” hive they now have access to a sharing of population and resources from their Mother Hive.

Once these queens are all present, and there's enough present Jelly and Biomass. The central queen who started it all may begin a final royal cocoon process of which she’ll come out as an Empress. Once an Empress is developed, she’ll destroy her old ovipositor and create a new one.

An Empress is the absolute pinnacle a hive can (currently) reach, and is the most dangerous stage one can reach too. At this point, a Hive has fully reached a status of becoming a Mega Hive and will typically require a nuke to be dealt with due to the sheer strength and map wide prowess.

Empress development should be avoided at all costs, or should be prevented if a queen is within the process of transformation through a cocoon. Attempting to beat an Empress isn’t an easy task.