Trills are from Trillius Prime in the Alpha Quadrant and have been trading with Earth since the 22nd Century before becoming members of the Federation. All Trills have spots, their patterns are unique to individuals but show tends between family members.
A minority of Trills have been found to contain a biologically independent lifeform inside an abdominal pouch. The Trill governing body has declined to elaborate further on the presence of the entity, beyond saying it is a tradition for a select few Trills to host these organisms. The relationship between the Trill and this lifeform is unknown; what is known is that the connections between host and parasite are extensive and that there is some form of symbiotic relationship between the two, from the presence of the ‘Symbiosis Commission’ being the overall powerful committee on Trill.
Trillius Prime itself is a warm, humid world with purple oceans. The Hoobishan Baths are renowned across the planet. Mak’ala is the capital city of the planet, where the Symbiosis Commission is headquartered. The Trill only recently signed up as full members of the Federation in 2285 after enjoying close relations for over a century and a half.
I am consciously choosing to ignore TNG: The Host in having the symbiont unknown until the 24th century, simply because any medical, scientific or transporter scan will show the presence of a biologically-separate being within a minority of Trills. Trill culture and the Trill Symbiosis Commission will demand a wall of silence on the reasons for the symbiont being present and, most especially, on what the symbiont does. It is just not feasible, realistically, to hide the presence of a biologically separate entity from the battery of sensors and telepaths on a starship. Any Betazoid will sense the two thought patterns, further reinforcing the problem.
Ambassador Curzon Dax
Curzon Dax has rapidly established himself as one of the foremost diplomats of the Federation. Utilising the previous relations Trill enjoyed with their independence, Dax has been able to build as rapport with the Klingon Empire, demonstrating a true understanding of their culture. He has a reputation as a womaniser, but his skills as a mediator and diplomat far exceed and compensate for this short-coming. He initiated the good relations with the Klingons at the Korvat Colony in 2289 and Dax represented the Federation at the Khitomer Conference in 2293.
Since that time, Ambassador Dax has assisted Spock in building upon the foundations of peace with the Klingons. Dax has met with the Klingons on both the Enterprise-B and the Excelsior, as well as at the second Khitomer Accords and meetings at Kronos. Ambassador Dax played a vital diplomatic role in the ISC Pacification War, helping to negotiate the ceasefire with the ISC, negotiating the phased drawdown of ISC forces and the location of the peace treaty at Nimbus III.