The Cycloids (also known as the Tricladar/Tricladiar) are a race of variable appearance and role, They appear to be a mostly sapient race, operating similar to Xenomorphs. (and potentially having already encountered them due to an easter egg in one floor texture on a secret map)
They have invaded earth on two known occasions, each time getting thwarted by Duke Nukem, They have a Heirarchical system, and appear to be composed of several assimilated races.
Every cycloid tends to have three digits to a hand, Is usually reptillian in appearance, and usually replace limbs with weapons. Females are generally blue, but this may just be one variation of Queen.
They are belived to lay eggs, which hatch either pregnators or Protozoid Slimers. Octobrains are usually seen near them, as caretakers.
It is also widely belived that they had enslaved the Rigelantians that first kidnapped the super-soldier Duke Nukem.
It is not known if their name is infact "Cycloids"- as the name comes from "Cycloid Emperor"- which may also instead imply the rotating Tri-claw prosthetics