A Consul was the highest magistrate of the Roman Republic. There were always two Consuls, elected for a single year term, equal in power and able to veto each other's actions, in order to prevent a tyranny.
Under the Roman Empire the Emperor served as one of the Consuls. Being chosen as the second Consul, the Emperor's colleague, was a great honor but carried little real power.
During the late Middle Ages, Italian city states revived the title "Consul" for their magistrates, not always restricted to the highest. From such usage in Genoa developed the modern use of "Consul" as a diplomatic officer lower than Ambassador.
In the late 18th and early 19th Century some regimes and rulers used "Consul" as the title of the Head of State, the most well known being Napoleon Bonaparte who was First Consul of France (1799-1804) before crowning himself Emperor of the French. However, the term universally lost out to "President" in short order.
Consul in The Disunited States of America
In an alternate where the United States fell apart in the early 19th Century, many of the states which assumed full independence emphasized this role by promoting the heads of their Executive Branches from "Governor" to "Consul". This usage remained widespread nearly three hundred years later.
Justin Monroe at first found very strange and a bit exotic the idea of the Virginia Head of State being called "Consul", which in the home timeline had been downgraded to a low-ranking diplomatic office. However, when planes of the Virginia Air Force passed overhead on a bombing mission into Ohio, Monroe realized that the Consul should be taken as seriously as any other Head of State involved in a war and controlling an army with modern weapons.
- Consul of the United States of Atlantis (Atlantis Series)
- Censor of the Federated Commonwealths of America (A Different Flesh)