It is the Devil who wants to get Pahom into his power. Early in the story the Devil overhears Pahom bragging that if he had enough land he wouldn't fear the Devil himself.
"All right," thought the Devil. "We will have a tussle. I'll give you land enough, and by means of that land I will get you into my power."
Through the Devil's aid, Pahom acquires more and more land, but it is never enough and it has as negative effect on his character. He becomes belligerent with the other peasants and is chronically frustrated and dissatisfied. Finally he learns of the availability of enormous tracts of rich land in the region inhabited by the Bashkirs. He goes there and makes a deal with the leaders whereby for a thousand rubles he can own all the land he can walk around in a single day, that is, from sunrise to sunset. He keeps seeing sites with trees or water or other desirable features which he would like to include in his holdings, and his greed causes him to make a wider and wider circuit. Then he suddenly realizes that it is getting late and he is a long way from his starting point. He has to start running although he is already exhausted, and he drops dead just as he reaches his point of departure.
His servant picked up his spade and dug a grave long enough for Pahom to lie in, and buried him in it. Six feet from his head to his heels was all he needed.
The story does not say whether the Devil acquired possession of Pahom's soul, but presumably that is what happened.