actually i will have to change my vote from Bjorn The Fell Handed to Captain Lysander of the Imperial Fists. The man is a ledgend.
He goes missing for something like 1000 years, comes out of the warp in orbit of an Iron Warriors stronghold, gets captured , is tortured for a month , he escapes despite many injuries.
Then he and several other Imperial Fists who were captured with him escaped, they were initially unarmoured and unarmed except for their fists and fury and there they were tearing through the streets of the planetary captial, creating a bloody trail behind them.
They make it back to the Imperial Fists alive in the transport they stole there they endured a 6 or more month period where they were tested both physically and psychically tested before the chapter were sure they were who they were. At which point Lysander was restored to the First Captaincy.
Within 6 months of this the man leads the Fists in an assualt against Malodrax, the planet where he was captured, and laid waste to it
Although Kayvaan Shrike is also a ledgend who goes where he is needed not where he is wanted by Imperial commanders. He goes to the planets that have been abandoned by an overstretched and uncaring Imperium. It is said that during the Targus VIII campaign that the Orks grew to fear the shadows
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