Warning: Possible SPOILERS for Star Trek: Discovery!
The fifth episode of Star Trek: Discovery, titled "Choose Your Pain," at last debuted a new member of the main cast whose name has been in the opening credits since the very beginning but fans had yet to meet: Lieutenant Ash Tyler (Shazad Latif). But the new crew member of the U.S.S. Discovery arrives surrounded by controversy and suspicion: is Lt. Ash Tyler who he says he is or is he someone else entirely?
When Captain Lorca (Jason Isaacs) is captured by a Klingon prison ship commanded by L'Rell (Mary Chieffo), he is placed in the same cell as Lt. Tyler and notorious intergalactic con man Harcourt Fenton Mudd (Rainn Wilson). Tyler identified himself as a former crew member of the U.S.S. Yeager, under the command of Captain Steven Maranville. According to Tyler, he was taken prisoner when the Yeager was destroyed at the Battle of the Binary Stars. He claims he has been held in this prison ship for seven months - the entire length of the Klingon War thus far - and that he's survived so long relatively unscathed because L'Rell had 'taken a liking' to him, implying sex for favors, which Lorca taunted L'Rell about when he was later tortured by her. Tyler ultimately helped Lorca escape the Klingon ship, both leaving Mudd behind. During their escape, Tyler confronted L'Rell and savagely attacked her, before Lorca shot and injured L'Rell so they could steal a Klingon Raider.
Many fans aren't buying Tyler's story, which is full of holes and contrivances. Interestingly enough, Lorca himself doubted Tyler's tale. When Lorca asked him how he survived Klingon torture for seven months and Tyler said, "I'm tougher than I thought," Lorca immediately retorted "Or a liar." Despite what Lorca's instincts were telling him, Tyler seemingly earned Lorca's trust by helping him escape and reach the Discovery. If Lt. Ash Tyler isn't who he says he is, fans have a compelling theory as to Tyler's true identity:
"THIS MAN IS A KLINGON!"
Lieutenant Ash Tyler may in fact be the Klingon Voq in disguise. Voq is the albino Klingon who was torchbearer and devoted folllower of the late T'Kuvma (Chris Obi). Following the Battle of the Binary Stars, Voq and L'Rell were stranded with no functioning warp drive and no food. We even learned the gruesome truth that to fend off starvation, they ate the corpse of Captain Georgiou (Michelle Yeoh). When Kol of House Kor (Kenneth Mitchell) incited mutiny and took command of Voq's followers, Kol abandoned Voq to die on board the wreck of the U.S.S. Shenzhou. However, L'Rell, who has a romantic relationship with Voq, beamed herself on board the Shenzhou to share Voq's fate. When last we saw Voq, he was going through the still-functioning ship's log of the Shenzhou and learning all he could about Starfleet and the Federation. Voq's disapperance and L'Rell's sudden reappearance as commander of a prison ship opens up a slew of questions. How did they escape the Shenzhou? How did L'Rell assume command of the prison ship? And how did L'Rell learn to speak English as well as she did when she tortured Lorca?
All of this very easily and credibly leads to the possibility that Ash Tyler is actually Voq in disguise. L'Rell told Lorca she was descended from spies - she is from House Mo'Kai, known as "watchers," "deceivers," and "weavers of lies" among the Klingon Empire. It's very possible Lt. Ash Tyler is Voq surgically altered to appear human and sent as a Klingon infiltrator to the Discovery. The capture of Lorca was likely no accident nor a stroke of luck - he was targeted so Voq-as-Tyler could gain his trust by helping him escape the Klingon ship and join him on board the Discovery. While it's unclear just how long L'Rell and Voq were trapped on board the Shenzhou and when in the course of the seven months between "Battle at the Binary Stars" and "Choose Your Pain" they could have escaped the Shenzhou and surgically altered Voq to pass for human, with L'Rell's background as a spy, they had the necessary intel from the Shenzhou to implement such a plan.
There have been numerous instances of Star Trek characters being surgically altered to pass for an alien race to perform espionage, starting with The Original Series' Captain Kirk (William Shatner) undergoing surgery to become a Romulan and steal a cloaking device in season 3's "The Enterprise Incident." Counselor Troi in Star Trek: The Next Generation also once had to pass as a Romulan, while Captain Sisko (Avery Brooks), Miles O'Brien (Colm Meaney), and Odo (Rene Auberjonois) were surgically altered to become Klingons on an espionage mission on Star Trek: Deep Space Nine. Probably the most famous Klingon who was altered to pass as a human was Arne Darvin (Charlie Brill), who appeared in The Original Series episode "The Trouble With Tribbles" and then led the Deep Space Nine crew into a time travel chase back to Kirk's era in "Trials and Tribble-ations". Star Trek: Enterprise also introduced the Augment Virus to explain why Klingons in The Original Series look and sound more human than other Klingons. It's likely no coincidence that Lorca keeps a Tribble in his ready room; if Tyler is indeed a Klingon, the Tribble should ultimately be what sounds the whistle and exposes Tyler as Voq.