Complex sentence: The title the "White Sultan" was regarded with bemusement by Landon, who maintained that Sultan Qaboos was very much in charge of Oman's destiny, and he was simply a servant and friend there to give advice.
Split into simpler sentences: The title the "White Sultan" was regarded with bemusement by Landon, who maintained that His Majesty Sultan Qaboos was very much in charge of Oman's destiny. Landon was simply a servant and friend there to give advice.