Lieutenant Lech Kril is the boss of Mars, and also appears on Ceres in a dual boss fight with Captain Vor. He is a decorated war hero of the Grineer, with full-body armour that grants both cold- and heat-based abilities.
He is not very involved in the lore of the Tenno's journey. Besides his appearance on Mars, he is mentioned briefly in the Codex entry of Executioner Gorth, and his appearance with Captain Vor is implied to be the result of Operation: Arid Fear, when the Grineer needed to shore up the security of their settlements after the Tenno discovered their locations. Why the duo are now on Ceres is unknown. Lech Kril is mentioned by Tyl Regor during Mirror Defence missions, where it is reiterated that Mars is Kril's jurisdiction.
Lotus: "Lieutenant Lech Kril has been implicated in a Grineer plot to annihilate one of our remote colonies in this sector. The plan is to alter the course of a rogue asteroid which will put the colony directly in the planetoid's path. Locate and eliminate Kril."1
Lotus: "Kril is a seasoned war hero with many battles under his belt. His victories are decided by his trusty hammer, one which he wields with brutal consequences."
Lotus: "Kril is highly unpredictable. We suspect he may have other tricks up his sleeve. To survive this battle, you must strike hard and fast."
Lotus: "Eliminating Kril is the only chance for our exposed colony."
Lotus: "You are nearing Kril's location. Proceed with caution."
Lotus: "Kril is aware of your presence. Strike first."
(mission complete) Lotus: "The death of revered war hero Lech Kril will undoubtedly send shockwaves throughout Grineer society. The silencing of his hammer will bring security to this system, but we have potentially created a martyr in Kril."
Lech Kril: "And I will strike down upon [name] with great vengeance and furious anger!"
Lech Kril: "The sound of hammer shattering ice is pure auditory perfection."
Lech Kril: "Beneath those suits exist flesh. Flesh bleeds. [name] bleeds."
Lech Kril: "I have seen and conquered many clans. [clan] will be next!"
Lech Kril: "Does that second skin peel away just as easy as the first?"
Lech Kril: "Grineer immortality begins with the strike of my hammer!"
Lech Kril: "I forgot my nails… I guess [name] will have to do!"
Lech Kril: "I am Lech Kril. My hammer awaits your skull."
Lech Kril: "Trust me when I say you won't feel a thing."
Lech Kril: "You ever get hammered in that suit?"
Lech Kril: "Hold still and I'll make this quick."
Dual boss fight
During the dual boss fight with Captain Vor at Exta on Ceres, each target still has their own dialogue from their respective Assassination missions, but the Lotus will give target backgrounds specific to the mission.
Lotus: "This is your most dangerous assassination yet. Captain Vor has teamed up with Lech Kril to take you down. Let's show them your true Tenno power."
Lotus: "Vor and Kril are waiting for you. I recommend you focus your attacks on one target. If you split your attention, you may fail."
Lotus: "Vor's mobility could make him the larger threat. Observe their attack patterns and look for an opportunity to divide and conquer."