This is adopted from Element Masters/ GateWar RPGs

Observers are three and a half feet (1.2 meters) tall humanoids. Their skin is milky white and very smooth (except around the joints, where it is slightly wrinkled). They have no visible or known sexual organs. There feet are fairly oversized. Their hands are normally clasped behind their back.

Their flatish heads are dominated by two huge eyes (which can see in the entire electromagnetic specturm, and can do spectral anaylsis). They have tiny slit noses and no real mouth. They can hear, but have no observable ears (perhaps their eyes pick up the vibrations?)

They communicate with each other, when that happens, by staring in each others eyes. Sometimes small flashes of light are seen.

Observers do not eat, sleep, nor excrete. Breathing seems to be an optional behavior. They generate a nearly impenetrable forceshield. Perhaps they are absorbing ambient energies and focusing them. The theories vary.

Additional Information
Observers do nothing but observe. They waunder the world watching. Sometimes they will stay in one area of interest or following an interesting individual or group. They seem to witness history and remember it. People often take great pride in the fact that Observers find them interesting enough to watch.

Observers were obviously made for this task. Who made them and who is record of history is currently unknown.