Lieutenant-Colonel Martin Michael Charles Charteris, Baron Charteris of Amisfield, was a British Army officer and courtier of Queen Elizabeth II. Charteris was the longest-serving Assistant Private Secretary to the Sovereign, having served for over 18 years in that position. Later, he became Private Secretary to the Sovereign.

Elizabeth II was Queen of the United Kingdom and other Commonwealth realms from 6 February 1952 until her death in 2022. She was queen regnant of 32 sovereign states over the course of her lifetime and remained the monarch of 15 realms by the time of her death. Her reign of 70 years and 214 days is the longest of any British monarch or female monarch, and the second longest verified reign of any monarch of a sovereign state in history.