One of the non-human beings that are often encountered are described as 'Reptilians'. They are commonly encountered, e.g., during abductions.

Galactic lore claims many of these reptilians belong to the Draconian / Orion Confederation. They are usually characterized as a bunch of aliens with evil intentions, i.e. to conquer and control as much of this galaxy as they can. (In her books, Barbara Marciniak refers to them as 'Lizzies'). 

These reptilians supposedly are coming from: Thuban (Alpha Draconis) & Tiphon (Draco), Bellatrix & Rigel (Orion), Epsilon Bootes, Zeta Reticuli and Altair (Aquilla).

Note, however, that there also are stories in the Galactic Lore about friendly reptilian races.

Apart from these off-world reptilians, there also are persistent world-wide stories about a reptilian race that is native to Earth, and that would live in a network of underground cities. (See Agartha). As such they meet the criteria for a Breakaway Civilization.

Physical appearance:

There are several lizard races, including insectoids, reptoids, dinoids (or saurians, as some people prefer to call them), as well as cross-breeds between them.

The most common species are:

For more information about their appearance, read the topic 'Reptilian phenotype'.

See also: Draco, Orion, Vega, Zeta and Altair.