“You're not supposed to be in here! You're going to ruin the surprise!”The following section contains spoilers.
“Orokin secrets cannot remain secret forever! Start talking!”The following article/section is conjecture. Content is subjected to change/removal as the game progresses. Please do not use this article for critical in-game information.
Dr. Tengus is a renowned Grineer scientist, known amongst the Tenno as the Director of the Grustrag Reconditioning Facility and for callous innovation and remarkable creativity on the subject of genetics and psychology.
Dr. Tengus is a character that was introduced in the backstory of The Grustrag Three serving under Councilor Vay Hek. Chronologically, however, Tengus is first mentioned to the Tenno by Grineer Soldiers overheard talking on the battlefield in the Once Awake Quest.
While little is known about this character, Dr. Tengus is of importance to the Warframe universe, being the sole cause for the return of the Infestation to the Solar System. Dr. Tengus is also behind the creation of Councilor Vay Hek's cybernetic body, after the latter was heavily wounded by Grineer Ghouls during his presentation to the Grineer Queens. He also took in three faulty Grineer; Vem Tabook, Leekter, and Shik Tal, modifying the blood thirsty soldiers into The Grustrag Three.
The G3, originally serving under General Sargas Ruk, were committed to Tengus' facility for permanent incarceration, after slaughtering their fellow combatants. However, Dr. Tengus saw potential in the G3, namely their combat abilities, and made a recommendation to Vay Hek that they be reconditioned to focus their aggression elsewhere.
Dr. Tengus was successful in turning their violent tendencies toward the Tenno and soon handed them over to Councilor Vay Hek, but regretted to inform that the reconditioning did not completely remove their violent action toward fellow Grineer. The means by which he circumvented this problem was by inventing the Grustag Bolt, which weakened the wearer's ability to harm Grineer. Producing a surplus of these Bolts, Tengus suggested to Vay Hek that he use them to weaken the Tenno, should the Grustrag prove successful in the field.