Colonel West in the Federation President's office.
Colonel West disguised as a Klingon assassin.
Colonel West was an officer in Starfleet's military forces in 2293. He was part of a group of Federation personnel involved in the Khitomer conspiracy that attempted to destabilize the peace negotiations with the Klingon Empire.
West helped prepare and present Operation Retrieve, the aborted mission plan to use a military incursion to rescue Kirk and McCoy from Rura Penthe, a Klingon penal asteroid. When asked what would happen if the operation provoked a full-scale war, West confidently commented, "...we would clean their chronometers."
Colonel West was killed as he attempted to assassinate the Federation President during the Khitomer Conference, disguised as a Klingon warrior. (Star Trek VI: The Undiscovered Country)
Background
Colonel West was portrayed by Rene Auberjonois, who would later portray Constable Odo on DS9.
Named after Lt. Colonel Oliver North who participated in the Iran-Contra scandal. (North/West)
West never actually appeared in the theatrical version of Star Trek VI since his scenes were deleted. However, he can be seen on the VHS and DVD releases of the movie, but is not listed in the cast credits at the end of VHS or DVD.
While identified in dialog as a 'colonel' (a military rank not contained in Starfleet's naval system, perhaps implying that he was a member of - as has been often suggested in the FASA RPGs - a Starfleet equivalent of the Marine Corps), West wore the uniform of a Starfleet vice admiral (equivalent to a lieutenant general). This is probably a costuming error, as, assuming he was part of a Starfleet military force, the rank equivalent to a military colonel would be a naval captain, he should have a similar insignia worn by Kirk and the other captains of this era.
There is a military practice known as "frocking" that allows an officer to fill the billet of a higher rank on a temporary basis. These frocked assignments are usually only made to fill a critical vacancy in a time of emergency or war. Such an officer would wear the uniform of the higher rank and enjoy most of the privileges of that rank for the duration of the assignment. This type of temporary ranking is also known as a "brevet commission".
There is another practice for an officer ranked higher than colonel being referred to as such - in the British army, a general officer (equivalent in rank to an admiral officer, that West wore the pin of) can be called colonel as a titular commander of a regiment. The full title given to said general is "colonel of the regiment".