Kol (Klingonese spelling: qol) was a Klingon warrior who lived during the mid-23rd century. Kol represented the House of Kor on the Klingon High Council in 2256. He also commanded at least two different Klingon starships.
When T'Kuvma rallied the twenty-four Great Houses by using the Beacon of Kahless in 2256, Kol's vessel answered the call. Irritated at T'Kuvma's initial absence from the communication between his ship and the High Council, Kol demanded his presence. When T'Kuvma did appear and belittled their concerns, Kol demanded that he show respect, as T'Kuvma was not a member of the High Council.
As T'Kuvma laid out his desire for uniting the Klingon people, Kol scorned at the presence of outcasts from Klingon society, and warned T'Kuvma that he would one day put him in his place, before cutting communication. (DIS: "Battle at the Binary Stars")
T'Kuvma died before Kol could carry out that threat. However, Kol later transported aboard the Sarcophagus and bribed its starving crew with food, causing them to abandon Voq (T'Kuvma's protege) and follow Kol instead. Kol ordered L'Rell to immediately kill Voq. However, L'Rell was able to convince Kol to exile Voq to the wrecked USS Shenzhou. (DIS: "The Butcher's Knife Cares Not for the Lamb's Cry")
Kol later consolidated his power over the High Council and expelled all Great Houses that were not allied with him. Kol spread the rumor that two renegade Houses, the House of D'Ghor and House of Mókai, were seeking an alliance with the Federation, in an attempt to lure a high-level Federation operative into a trap. Kol had sought to capture Sarek, but Admiral Katrina Cornwell was sent in Sarek's place. Kol had Cornwell's security escort killed and the admiral was imprisoned aboard the Sarcophagus. (DIS: "Lethe")
Kol remained onboard the Ship of the Dead as he prosecuted the war. At some point, he acquired Philippa Georgiou's Starfleet insignia, and carried it with him. (DIS: "Into the Forest I Go") He had begun dispersing the Sarcophagus' cloaking technology to ships loyal to him, enabling the Klingons to ambush three Starfleet ships on patrol. Unlike T'Kuvma, Kol sought not unity, but his house's rule over the Klingon Empire, and the Empire's supremacy over the Federation. When L'Rell returned to the Sarcophagus, Kol accepted her offer to take over the interrogation of Cornwell as a way for her to prove her usefulness to his cause. However, he later discovered L'Rell and Cornwell in one of the ship's corridors, and demanded to know where she was taking the prisoner. When the two fought, he instructed his guard not to interfere and watched as L'Rell seemingly killed the Starfleet admiral.
L'Rell then reported her findings from her interrogation – that the USS Discovery carried new technology which could be used to the Empire's advantage, at which Kol berated her for her recklessness in allowing the admiral to escape. When L'Rell attempted to leave, Kol ordered her to stop. He noted that a skilled interrogator would be needed in the future, and marked her as a member of House Kor, demanding her loyalty, which she gave. Then, telling L'Rell that he had seen through her deceit, he instructed two of his people to "show her how House Kor treats liars," after which the pair dragged the Klingon female away. Upon being told of a communication from the planet Pahvo, Kol ordered his ship there immediately. (DIS: "Si Vis Pacem, Para Bellum")
Arriving at Pahvo, Kol was informed that the Discovery had appeared in orbit, an action he considered foolish. He announced his intention to board Discovery, eliminate its crew, and capture its technology, before destroying the planet and its inhabitants. His crew expressing its support, the Sarcophagus then decloaked and opened fire on the Starfleet vessel.
As the Discovery began using its spore drive to outmaneuver the Klingon ship, Kol ordered the cloak reengaged. Believing the Starfleet ship's actions to be a ruse of some sort – in reality, the ship was engaging in multiple jumps to develop an algorithm to penetrate the cloaking screen – Kol ordered his crew to leave the system. He was prevented from doing so by the appearance of Michael Burnham, who had infiltrated his vessel. Using a universal translator to speak in Klingonese – something which Kol verbally attacked as another attempt by the Federation to subsume Klingon identity – Burnham identified herself as the person who had killed T'Kuvma.
Although goading Burnham using Georgiou's insignia, and being goaded in turn about his absence at the Battle of the Binary Stars, Kol recognized the value of Burnham's capture to his ongoing consolidation of the Empire, as he expected it would sway the remaining T'Kuvma loyalists to his side. He ordered her to be imprisoned, but Burnham challenged him to single combat to prove his worthiness to capture her. Kol then tossed one of his mek'leths to Burnham and accepted her challenge.
Kol was quickly able to overpower the Human, disarming her and grabbing her by the throat. He gloated that her death would secure his position as absolute ruler of the Empire; however, before he could deliver the killing blow, Burnham seized Georgiou's insignia and jumped off the bridge's mezzanine railing to be beamed away.
Meanwhile, Burnham's combat with Kol had given Discovery enough time to complete the algorithm. With the Klingons' cloaking technology exposed, the Discovery launched a final attack on the Sarcophagus, killing all aboard, including Kol. (DIS: "Into the Forest I Go")
Background information Edit
Kol was portrayed by Kenneth Mitchell.
Originally, CBS announced in December 2016 that Kol, who was at that point going to be a "protégé of T'Kuvma", was to be played by Shazad Latif. In the final version, Latif went on to portray Ash Tyler, while the role of T'Kuvma's protégé was given to another Klingon named Voq; Kol, meanwhile, became the leader of a rival Great House. 
When he tried out for the part, Kenneth Mitchell wasn't completely au fait with the role. "When I auditioned, I didn't know I was auditioning to be a Klingon," he clarified. (Star Trek Magazine Discovery Collectors Edition, p. 44)
During his Klingon makeup application process, Kenneth Mitchell usually concentrated on running over his lines of Klingonese dialogue. His family considered him insane for spending so much time on learning the Klingon speech. However, he believed that those lengths he went to were ultimately worthwhile. (Star Trek Magazine Discovery Collectors Edition, p. 44)