Vrenn is the main character in the imagined novel "The Final Reflection", a novel about the Klingons in the early stages of the Federation, in the early 2200s.
The novel follows Vrenn's career. He was adopted by (Thought-Admiral) Kethas epetai-Khemara from House Gensa, a "House of Lineless Youth", in the mistaken belief by Kethas that he was the last survivor of the line Rustazh. Kethas took Vrenn in the memory of his supposed father - Kovar.
As he had no living children of his own, Kethas made Vrenn sole heir to the House on the condition that he forget his Rustazh lineage.
" Vrenn replied " I was never Rustazh until now....but now I am already Khemara"
Vrenn Khemara served his cadet cruise on the IKV Blue Fire under Squadron Leader Kodon, raiding Romulan space. A brawl found him unexpectedly promoted to the Bridge crew, and a promising career was born until it becase clear that his connection with Kethas put him in danger.
Quickly, he was promoted to command of a Scout ship on "The frontier" to get him out of the way and took the line-name Rustazh as "...it was free to use".
Krenn tai-Rustazh quickly developed a reputation as a brave and strategic captain, and was selected to lead a mission to pick up the first Federation Ambassador to the Klingon Empire, Emanuel Tagore, with whom he and his command crew developed a friendship.
Krenn took Tagore back to the Federation some 5 years later at a time when the Federation looked as if it was about to break up. Krenn represented the Empire at a conference known as "A Babel" and was instrumental in revealing a militaristic plot by some Starfleet officers to trigger a war with the Empire to keep the Federation together by fear of conquest.
In his time at the conference, Krenn played chess with a young half-Vulcan named Spock. Krenn thought "that one is worthy of the stars". (TOS novel: The Final Reflection)