The Lizardmen are a faction in the fictional Warhammer Fantasy setting, and an army in the tabletop wargame Warhammer Fantasy Battle (based in the same setting), which is created by Games Workshop. The Lizardmen forces have a mesoamerican / Aztec themed culture, and are composed of various reptilian and amphibian creatures, including many based on dinosaurs and pterosaurs.
In earlier versions of the setting (up to and including the 3rd edition of Warhammer Fantasy Battle and the 1st edition of Warhammer Fantasy Roleplay) there was a separate Slann army based in Lustria. The background story of the Warhammer world described its creators as the "Old Slann" or "Old Ones" interchangeably. These were the ancestors of the current Slann, froglike creatures who once ruled Lustria in a great empire with an Inca, Aztec and Maya feel, leaving behind a legacy of high-tech/magical items called Power Weapons, made of a mysterious black substance. Forces available to this army as allies or enemies included humanoid pygmies with blowguns and Amazonian warrior-women, as well as lobotomised slave-soldiers.
The Old Ones are a mythical and mysterious race or possibly a group of distinct species in the table-top wargame Warhammer 40,000. They played a pivotal role in the history of many races, including the Eldar, Jokaero, Humans, Orks and Necrons.
The Old Ones of Warhammer 40,000 history are possibly an ancient species of nearly immortal, cold-blooded beings, who were probably the first race in the galaxy to have evolved sentience (however, the C'tan predate the Old Ones, but the C'tan didn't partake in the affairs of the Galaxy until the Necrontyr gave them physical bodies just before the War in Heaven). A supposedly benevolent and gentle race, they appear to have wished to nurture the younger races and protect them from the C'tan. The Old Ones were inherently patient as a race, and before attempting to explore the galaxy they made an extensive study of astronomy, which led them to discover the Immaterium. At the time, the Immaterium was as yet unaffected by the psychic emissions of other intelligent races, and so it was a calm and steady realm. The Old Ones were able to exploit the Immaterium, allowing them to travel across the galaxy at a whim without the need of starships.