Omega Hunters were originally designed to be extremely massive, chunky robots in a similar manner to the Sentinels from Marvel Comics but later changed design to resemble more closely the original intent of a humanoid skeleton (albeit with some obvious modifications).
Omega Hunters are vicious, deadly machines that track down beings with powers or gifts that may be of use to the Invasion Force and give them a brutal choice - to serve or die.. if they willingly surrender they are made into Trackers (basically slaves) and forced to wear Mind-Collars that bind them to the Invasion Force, if they refuse they are executed without mercy by the Omega Hunters.
The Omega Hunters, like all other Invasion Force members, are subservient to Noah Adam Man - the main antagonist of the entire series.
The first Omega Hunter seen in the series was a large model that pursued the unfortunate Alley-Cat on her first date with then pre-mate (boyfriend) Max, chasing her into an alley it proceeded to open fire on her and caused her to activate her hybrid ability for the first time - which also saved her life as the Omega Hunter's gunfire was rendered useless due to her intangibility.
However the Omega Hunter would not relent until it was ultimately destroyed by the Solar Foxes, who arrived to rescue Alley-Cat - this would in turn lead to the mass breakout that formed the original Extinctioners team.