They are about the size of a large Human and possess a great deal of strength. They are naturally aggressive and prone to internecine strife which affects their ability to expand. They share a similar disposition as the Klingons with an intense love for combat. They are also noted as being quite brutal as well as extremely violent in their dealings with other races. Though this is the case, the Lyrans are well acquianted with the saying of "an enemy of my enemy is my friend." As such, they were known to be allies of the Klingon Empire and the two aided each other numerous times.
Hydran scientists believed that there was genetic evidence to suggest that the Lyrans and the Mirak were related, something that greatly insulted both races and even sparked a war between the Hydran Kingdom and Lyran Star Empire.
The Lyrans were known to be bitter enemies of the Mirak species with contact between the two almost always being dangerous if not deadly. Klingon warriors were noted as saying that it was better spending time in an interrogation booth rather then be caught in the middle of a Lyran-Mirak blood feud. (TOS video game: Starfleet Command)
- Note that the Starfleet Battles universe listed that it was the Kzinti the Lyrans had a blood feud with, however, due to legal problems, the creators of the game were not able to use the name Kzinti and instead renamed the race as the Mirak.