From SA Mafia Wiki
A Governor is a role which can "pardon" executions, causing the hammer on a particular player to fail. The Governor typically is contacted by the moderator after an execution has been made but before flavor and flip are posted, asking if they would like to cancel the vote. If yes, typically the day then ends with a No-Hang, generally with no explanation given for why the player was not executed that day. Occasionally a Governor can even commute the execution onto a different player of their choosing, but this is not common.
Governors are typically given restrictions, such as only being able to pardon a player once, or not being able to pardon themselves.
Note that this is not to be confused with the similarly-titled Politician role.