Knight-Marshal of Krondor was the most important military leader in the West after the Prince of Krondor. One of the two of them carried the title Marshal of the Armies of the West in time of war, and historically it was the Knight-Marshal as often as it was the Prince.
By tradition, the Knight-Marshal of Krondor held rank equal to that of a Duke, and occasionally in the past, the Duke of Krondor had held both offices.
The Knight-Marshal, also known as Military Commander of the Principality has control of vassal garrisons to Krondor such as in Durrony's Vale and Malac's Cross.
It is not known if the King had his own Knight-Marshal for Rillanon or even if other Duchies or Baronies had their own Knight-Marshal. (page 312 "Magician's End; "…Knight-Marshal of Silden, Geoffrey du Gale…").