Kryptman

"'My opinion IS; straight-laced, self-strangulating sheeplings slapping heresy on anything even halfway logical is what brought us into this mess in the first place. Maybe taking two seconds to consider options that aren't 'purge this', 'cleanse that', and 'burn burn burn!' might prove beneficial, even if you don't wind up doing it.'"Fidus Kryptman is a former Inquisitor of the Ordo Xenos. He played a significant role in discovering the emerging threat of the Tyranids.

Official Canon
Kryptman was the first to discover the Tyranids when he found the planet Tyran to be stripped of all life forms. Realizing that the new Xenos threat was headed for Ultramar, he warned ahead of the impending attack.

Throughout the course of the three Tyrannic Wars, Kryptman learned as much as he could about the enemy. He came to the conclusion that the only practical way of stopping the threat was to Exterminatus every planet in their path, hopefully starving them out by denying them biomass. Such a move proved to be too much for even the Inquisition, and he was exiled for his actions. Despite this, the Deathwatch sought him out as they were confounded over the activities of hive fleet Tiamat, as the Tyranids were constructing a powerful psychic organism in the Tiamat system.

BEHEMOTH Canon
Kryptman is seen as a highly eccentric and short-tempered Inquisitor who treats his Deathwatch marines like personal servants, having them make him his recaff for him. His initial investigation into the planet Tyran was to find out why his shipment of new glasses was delayed; something that proved to be very aggravating for Kryptman, as the only other pair he had were sunglasses. He wanted to call the Tyranids the “Space Bugs of Death,” but was turned down by the others.

During his investigation, he had his xenobiologist Draken work on finding a weakness for the Tyranids, while he busied himself watching confiscated Xenos erotica, for research purposes. Eventually he found the next target for remnants of hive fleet Behemoth, and with the help of the Blood Ravens and his Deathwatch team, they prepared to intercept the incoming fleet. However, he unsubtly suggests that if they fail, he’d simply Exterminatus the planet, with his men doubting that they’d even consider giving them enough time to evacuate. However, Kryptman discovered that Draken betrayed him, as he planned on drawing the Tyranids instead of repelling them. Draken’s treatchery was quickly stopped; however, the hive fleet had already arrived.

Kryptman admitted that he knew all along that Draken was once part of a dangerous Xenos species, and only kept it secret to avoid the possibility of costly lawsuits. He even told one of his stormtroopers that because he already knew too much he was going to have to execute him, so he might as well hear the whole story. They were shortly attacked by Genestealers, but Kryptman killed the stormtrooper all the same after they survived the attack.

Kryptman's ship was destroyed by the invading Tyranid fleet before he had a chance to pre-emptively Exterminatus the planet, causing him and his team to fall victim to the Norn Queen's overwhelming psychic presence. However, his rage at having all of his "xenos research material" (read: xenos erotica) destroyed allowed him to overcome the Norn Queen's powers, giving his team the chance to kill the Norn Queen. However, he and his team were unable to kill the newly arrived Swarmlord, and were nearly killed before Marneus Calgar arrived to finish the job. Despite their victory, Kryptman had a premonition that the Tyranid menace was far from gone, having seen the very face of the Tyranid Hivemind during the psychic assault.

TTS Canon
Kryptman suddenly appears among the exiled Inquisitors during their visit to Commorragh, sharply demanding that the other Inquisitors shut up so that he could speak. Inquisitor Toddler-on-the-Ground refused to listen to the disgraced Inquisitor, so Kryptman shot him in the kneecaps. Kryptman said that the fact that nobody even noticed his presence before now was proof of their incompetence, and that he’d support whatever decision the Fyodperor would make. The Emperor liked Kryptman’s candor and cool-headed approach. But when told by Rogal Dorn and Custodisi about Kryptman’s genocide and exile, the Emperor refused to retract his statement and claimed that “he must have had a good reason.”

Trivia

 * While Kryptman makes his first formal appearance in TTS in episode 26 Part 2, his first real appearance in TTS is a cameo in Episode 24: Of Khans and Cages (Specifically at 23:27, briefly appearing from behind his Deathwatch retinue (the exact same ones that appeared with him in BEHEMOTH)).
 * Eliphus gave Kryptman a bionic nose because he thought it would be funny.