Dao (symbiont)

From Hidden Frontier

Dao is a Trill symbiont who is illegally joined with Trill Jorian Zen, its 18th host. The illegal joining was caused by falling so deeply in love with a woman in its 16th life that it affected its 17th incarnation, Cassius Dao. It led Cassius to break the Trill taboo against reassociation, which forbids joined Trills from re-establishing intimate relationships with people from its former lives, resulting in Dao's exile from Trill society. ("The Battle Is Joined")

Dao was noted for its research in hyperdimensional physics over the course of five lives at Trill's Institute for Hyperdimensional Studies. Interestingly, many of the Institute's personnel reassociated because their hosts continued their hyperdimensional research over multiple lives, but this "exception" appears to have been kept secret from Trill society at large.