The Hegemony
The Hegemony is a highly advanced extradimensional civilization.  
Though their history dates back tens of millions of years, very little is
actually known about them.  In their natural habitat, the aliens likely
exist in a partially non-corporeal state, and share consciousness with
several other individuals.  They are unable to maintain this form
outside of their realm; when they transition into the normal universe,
the aliens manifest themselves as grotesque pillars of rotted flesh.  In
this form, the aliens are virtually indestructible and able to elude
most sensors.  (“The Treachery of a Queen” [TFF], “Where Angels
Fear to Tread” [TFF]).  Their genetic code is nearly three times more
complex than an average humanoid (“Scorpion, part I” [VGR]), and
served as a template for the creation of Species 8472.  (“A Link to the
Past” [TFF]).

Approximately one million years ago, the Hegemony constructed an
immensely powerful vessel—later known as the Necropolis of Ru’Hmet—
to explore other dimensions.  However, the Necropolis somehow
transitioned into normal space before the Hegemony could provide a
crew.  Because they were not able to exist in normal space, the
aliens could not pursue the Necropolis.  They were ultimately forced
to erect an Otherwordly Gate, which granted them entry into normal
space.  Several vessels were sent through the gate to search for the
Necropolis, however, none were successful.    (“Words Better Left
Unspoken” [TFF], “Where Angels Fear to Tread” [TFF]).

Two hundred thousand years ago, a vessel commanded by General
Ordikan was captured by the Phobian Republic in the Sra’xa’diin
Nebula.  The Phobians were impressed with the technology aboard
the ship, and ultimately able to genetically modify the ship’s organic
components to create a virtually indestructible race of warriors.  
Though the Phobians referred to these new aliens as the Sra’xa’diin,
they would later become known as Species 8472.  Helpless to stop the
Phobians, Ordikan and his partners watched as the Phobians used the
Sra’xa’diin to eliminate their blood enemies, the Al-Bhed. However,
the Sra’xa’diin did not stop there—they ultimately turned on their
masters and destroyed the Phobian Republic itself.  In the wake of
this incident, Ordikan vowed to restore the Phobian Republic.  The
Hegemony initlally agreed, but after tens of thousands of years
without progress, their support for the project waned—and they
recalled Ordikan to the Otherworldly Gate in 2399.  (“Words Better
Left Unspoken” [TFF]).

In the year 2400, the Hegemony made a complete and total
withdrawal from normal space when they learned the Necroplis of
Ru’Hmet had come under the control of the Elorg Bloc.  Fearing the
destruction of the Milky Way, they forever vacated the material
realm.  (“Where Angels Fear to Tread” [TFF]).
The Necropolis of Ru'Hmet
Phobian Vessels flank Eredas-Il