The Romulan ambassador to the Federation in 2293, who sits in on the President's most secret briefings while conspiring with Cartwright and Chang to wreck the Klingon peace in Star Trek VI.
Nanclus is the Romulan Star Empire's ambassador on Earth in Star Trek VI: The Undiscovered Country, played by Darryl Henriques.
After the assassination of Chancellor Gorkon he is a constant presence in the Federation President's office, hearing Sarek and the Klingon ambassador argue over the arrest of Kirk and McCoy and listening as Starfleet presents Operation Retrieve, its plan for a military rescue.
His apparent neutrality is a pose. When Spock forces a mind meld on Valeris aboard the Enterprise, she names Nanclus alongside Admiral Cartwright and General Chang as a leader of the plot, showing that hardliners in three powers had joined forces to keep the old hostilities alive.