In a timeline without Romulans, the Guidons ruled the supermassive Guidon Space Pontificate, which was a major power bordering the Klingon Empire. The Guidons had a reputation for dealing ruthlessly with those who disturbed them.
In 2293, the Interstellar Union intelligence service found out that the Klingon Empire had acquired non-aggression treaties with the Gorn Hegemony, the Guidon Pontificate, and the Holy Order of the Kinshaya. (ST - Myriad Universes novel: The Tears of Eridanus)
Their language consisted of a series of rapid squeaks, and they were known to "wildly gesticulate". They also had high-pitched voices. The Farrezzis' squeaking speech reminded James T. Kirk of Guidons, who had the highest-pitched voices he'd ever heard. (TNG - The Sky's the Limit short story: "Meet with Triumph and Disaster", TOS novel: A Choice of Catastrophes)