The Order of Kahless are a group within the Klingon Empire similar to the Order of the Bat'leth.
No details are known about the goal and purpose of the Order, however, it was known to be a highly prestigous group with only the best of Klingon's managing to enter it. Martok was inducted into the Order by Chancellor of the High Council of the Klingon Empire Gowron in 2375 when he was awarded the Star of Kahless. (DS9 episodes: "When It Rains...", "Tacking Into the Wind")