A governor was the head of government for a colony, province, or other sub-national body politic in the galaxy. There were several usages of the word throughout the Galactic Republic, Galactic Empire, New Republic and Galactic Alliance.
Governors existed in the Galactic Republic as it was a federal system, control of local systems and sectors were left to their own governments. It seems that the Old Republic only used governors temporarily, for systems that were unstable or for those that were newly-admitted to the Republic and lacked any capable governing system of their own. Mousul sought to get appointed sector governor of Ansion's region of space.
The one known example of an Old Republic governor was the Seswenna Sector, which was ruled by a governor and a lieutenant governor from at least 33 BBY until the end of the Republic. The governor and lieutenant governor of the Sector also simultaneously served as the governor/lieutenant governor of its capital planet, Eriadu.
The Empire left the self-government of many planets intact, especially those that were either indifferent or supportive of the New Order (such as Naboo and Corellia). Less than 1/80th of all planets had their governments altered. Planets that rebelled, were deemed hostile to the New Order, or newly-annexed by the Empire, had governors appointed. Some, such as Bakura, retained their government with only minor changes, but also had an appointed governor. The Empire also kept the position of Lieutenant Governor. Except for a few governors chosen by Palpatine, Imperial Governors were selected by the Imperial Ruling Council and received most orders from the Diplomatic Service. Emperor Palpatine had vague plans for eventually replacing the planetary governors with Dark Side Adepts, creating a "Dark Empire".
The New Republic's policy on governors (termed Governors-General) seemed to mirror that of the Old Republic. Both Corellia and Rhinnal had Governors-General, and at least Corellia's was elected by the planet's population. The Galactic Alliance continued the system, although several years after the end of the Yuuzhan Vong War it removed the Governor-General system from Corellia.
Governor-General was the title given to the Chief Executive Officer of the InterGalactic Company.
Officially, the Governor-General was the civilian Commander-in-Chief of the InterGalactic Company Defense Force. The position was referred to by a number of titles: Lord Governor, Governor-General, Emperor’s Representative, and Chief Magistrate. When addressing the Governor-General, they were referred to as Governor or Excellency more commonly by subordinates.
A Governor-General was elected by a "fifty percent plus one" majority vote of the InterGalactic Company Directorate. If the Governor-General was incapacitated, incommunicado, or dead, the Deputy Governor could then act as an interim Governor-General until the proper Governor-General returned or the Directorate could elect a new Governor-General.
The Governor-General could be recalled by a majority vote of the Directorate on presentation of a petition of no-confidence by a majority of the Governance and Operations Committee, or by a quarter of the primary members of the Directorate. The election of a Governor could be blocked by the Governance and Operations Committee on a unanimous vote. In practice, the power of the Governance and Operations Committee to void an election and initiate the recall of a sitting Governor-General meant any candidate proposed by or approved by the Governance and Operations Committee was likely to be elected by the Directorate. The Governance and Operations Committee consisted of the chairs of the Directorate committees and the Chair of the Directorate.