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 with the Klingons along 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. Nonetheless, the Lyrans are well acquainted with the saying "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 Kzinti 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 Kzinti 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 than be caught in the middle of a Lyran-Kzinti blood feud. (TOS video game: Starfleet Command)
- Note: Due to licensing issues, the creators of the Starfleet Command game were not able to use the name Kzinti and instead renamed the Kzin race as the Mirak.