An ancient speicies who lives on the other side of the galaxy. Somehow they know of the Federation and believe that it will take over the galaxy one day.
History
A ship was sent that took 248 years to get to Earth, so that it would destroy it. But the attempt was thwarted by the USS Phoenix-X. On thier way into Federation space, they disabled ships like the USS Cedar, the USS Blue Nose, the USS Shark, the USS Sun Light, and the USS Grolier. (PNX: "Bio Level 4")
Ancient Holy Scriptures
According to thier scriptures, which are nerarly 6000 years old - it was prophesied that the homeworld of Trozonia would be taken over by the Human species.