Pictured: The Executor, which served as Darth Vader's flagship.
In naval warfare, the term flagship denoted the personal starship used by a fleet commander who oversaw a group of naval vessels. The Executor-class Star Dreadnought known as the Executor functioned as both the flagship for the Dark Lord of the Sith Darth Vader and the command ship for Death Squadron. Conversely, the Ravager acted as the command vessel for Counselor to the Empire Gallius Rax and the Galactic Empire during the Battle of Jakku. The Eclipse was the personal flagship of Galactic Emperor Sheev Palpatine.
Admiral and later Fleet Admiral Gial Ackbar utilized the MC80 Star Cruiser Home One as his flagship, which also served as the command ship for the Alliance and New Republic fleets. During the Battle of Scarif, the MC75 Star Cruiser Profundity served as the flagship for Admiral Raddus. Furthermore, Phoenix Home_ was the flagship of Jun Sato, who was the Commander of the Rebel cell known as Phoenix Cell.
During the war between the First Order and the Resistance, the Supreme Leader Snoke's command ship, the Mega-class Star Dreadnought Supremacy, functioned as both the First Order's flagship and its mobile headquarters. In contrast, the MC85 Star Cruiser Raddus served as the Resistance's flagship. Both ships were severely damaged when Vice Admiral Amilyn Holdo of the Resistance crashed the Raddus through hyperspace into the Supremacy, bringing an end to the Battle of Oetchi.