Trion (species)

The Trions were a race of humanoids from the planet of the same name.

Biology
Trions looked identical to humans and could survive in similar conditions.

Culture
Trion society was for a long time constituted almost as a caste system, with much of the power and privilege the sole preserve of the ruling Clans. (TV: Planet of Fire) Different castes lived in different parts of the cities. (PROSE: Lords of the Storm) There were also shantytowns around the palaces. (PROSE: Zeitgeist) These clans were later overthrown, but the later regime was overturned, returning the Clans to power. (PROSE: Turlough and the Earthlink Dilemma)

Trions on the colonies had different traditions. On Sarn, they worshipped the fire god Logar, which was actually based on the memories of Trion vulcanologists. Those with the Misos Triangle were known as the Chosen Ones. (TV: Planet of Fire)

Trions used coins with two heads. (PROSE: The Eight Doctors)

Technology
The Trions were a reasonably advanced species, having space-faring capabilities and energy weapons. One Trion seemed completely unfazed by the fact that the Doctor's TARDIS had a dimensionally transcendental interior. (TV: Planet of Fire) Turlough was familiar with transmats. (TV: Mawdryn Undead)

History
Early in their history, Trion was invaded by the Tractators, an experience so horrific that for generations to come, an ancestral memory of it would be triggered at the sight of one. (TV: Frontios)

The Trions had had colonies planets for centuries. (PROSE: Lords of the Storm) This included Sarn, Darvey, Verdon, and New Trion. Some of these colonies, like Sarn, were abandoned over time. According to Turlough, the Trions had undercover agents on every civilised planet, including Earth. (TV: Planet of Fire) During Turlough's youth there was an uprising against the Clans, led by Rehtcaht. The Clansmen were deposed, their families broken up and sent to other planets - some Trion colonies, some not. These political exiles were marked with the Misos Triangle and were watched over by the Custodians. Rehctaht's tyrannical regime was eventually overthrown and the exiled Clansmen were allowed back on their original home. (TV: Planet of Fire, PROSE: Turlough and the Earthlink Dilemma)

About the same time, the Trion colony on Sarn was in danger from a volcanic eruption. Trion sent representative to save the colonists. (TV: Planet of Fire)

Behind the scenes

 * Since the nurse at Turlough's school had no problem when examining Turlough, that would imply that Trions have similar, if not identical, internal structure to humans.
 * Based on Turlough's comments, he may be older than he looks, implying a different rate of ageing.