A race of incredibly long-lived, elegant, effeminate individuals who go through several different occupational stages during their life. Often look towards the long-term future rather than the present. Prefer elaborate attacks by small bands of highly skilled fighters trained in powerful reality-altering powers activated through mental concentration.
A race which underwent large-scale civil war, but then reconciled and are obsessed with the greater societal good. Blood is bluish due to cobalt content instead of iron. Reality-altering powers are very rare. Invite outside races to join them in their society as well as military, the latter in which they are utilized as auxiliaries.
ET/Gray alien-looking race that favors careful investigation and planning followed by devastating surprise attacks and critical blows. Led by mysterious, cloistered individuals who wield enormous political power. Their history includes an ‘uplifting’ involving another race, though this is seldom spoken of for certain reasons.
Brutish, aggressive, hardy, battle-loving, relatively lower-intelligence and low-tech race that excels in combat, especially close-quarters. Individuals are tough to kill due to their internal physiology and can reach frightening sizes. Able to reproduce and mature quickly, meaning that an entire army can be raised within a few short generations. These facts lend to their use as a destructive force by other races, usually through bribery and/or careful manipulation. Will often descend into warring upon other members of their own race, sometimes just for the fun of it!
A race of metallic, artificially-created, robot-like beings who have the advantage of fantastically advanced technology – including interstellar travel accomplished through intertialess movement. Instead of combat specialists and vehicles, purpose-designed individuals serve these roles. Led by a race of extremely powerful, cunning, almost god-like beings (whom they practically worship and aspire to one day become) who manifest as mechanical monstrosities to wreak havoc against their victims. Individuals have low intelligence, but there are some specially-designed models with greater autonomy. Emotionless, they exterminate all organic life one planet at a time.
A race of insect-like creatures that may seem mindlessly feral, but are led and held together by a communal hive-mind. Totally absent standard technology, they rely completely on biological substitutes, with sub-types specialized for various combat and non-combat roles – including space flight! Poison and toxin spores are a favoured weapon apart from claws ripping directly into the flesh and metal vehicle plating of other races. At full strength and numbers, they pose an existential threat to every other race in the galaxy.
And don’t get me started about Starcraft!
Bald, scarred, experienced Space Marine in a power suit with a big a$$ automatic rifle who leads his squad into combat against the hated space aliens, following the command of of a younger hipster-looking commander.
See also related at Star Wars’ General Grievous = Warhammer 40,000′s Necron Lord, Drive Me Closer, I Want to Hit Them With My Sword and Brave Royal Malaysian Navy Heroically Rescues Hostages From Pirates – Using Suitcases Stuffed With Ransom Money! (heh!).