Celt

The Celts were a human ethnic group which inhabited Great Britain early in its history.

History
Pythagoras learned from the Celts. (PROSE: The Pythagoras Problem)

The Iceni, the Trinovantes, the Brigantes and the Catuvellauni were among the Celtic tribes which existed in Britain before and during the Roman occupation of the country, which began in 43 and lasted into the early 5th century. (AUDIO: The Wrath of the Iceni)

When the Romans drove the Celts out of England, they were allowed to settle in Avalon. (PROSE: The Shadows of Avalon)

In a timeline which might have been invalidated by Big Bang Two, the Eleventh Doctor suggested in 102 that a Celt may have damaged the Cyberman guard near Stonehenge in Wiltshire. (TV: The Pandorica Opens)

Celt worship
The Celts believed in multiple gods. (AUDIO: The Wrath of the Iceni)

Cessair was worshipped as the goddess Cailleach by the Celts, specifically the Druids. (TV: The Stones of Blood)

The Celts also thought of Saul as a local spirit. (PROSE: Timewyrm: Revelation)

The Celts considered the Bodach as evil spirits. The Celts possibly had a role in the construction of an obelisk and the Eye of Oblivion. (TV: Dream-Eaters)

Celts practiced human sacrifice, sacrificing people by burning them to death inside a wicker man. (AUDIO: Dead London)