The Trill are a humanoid species based on the planet Trill in the Alpha Quadrant, in which a small percentage of the population harbors a sentient lifeform known as a symbiont inside their bodies, a symbiotic relationship that plays a significant role in Trill culture and society. Such "joined" Trill have personalities that are a synthesis of the two beings, and can access the memories and skills of previous hosts.

Personality: Unlike Vulcans or Klingons, Trill do not really possess a stereotypical personality. As with Humans, their personalities span the spectrum. Like most other Federation members, they are generally optimistic, open to new ideas, and willing to help those in need.

Physical Description: Trill have the same average height and weight as Humans. Their skin tones range from pale pink to olive, but no darker; their hair, on the other hand, tends to be brown, black, or other dark shades. They have two rows of dark brown spots running from their foreheads down their bodies to their heels. Each Trill’s spots are as distinctive to him as fingerprints are to a Human.

Example Names: Trill place the given name before the family name. Joined Trill substitute the symbiont’s name for the family name. First names: Curzon, Joran, Tobin, Nilani, Emony, Ezri, Jadzia, Lenara. Symbiont names: Dax, Belar, Pren, Tigan, Otner.