What two characters or groups of characters from two different stories do something beneficial for Mars or the Martian race ?
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Characters whose actions benefit Mars:
The Martians in the story "The Third Expedition" create a familiar landscape in order to lull the Earth men into trusting them. By pretending to be their deceased relatives, the Martians convince Captain John Black and the other astronauts to abandon the safety of their ship and join them in a small town. In this story, the martians' actions benefit their race as a whole because they are able to deceive and kill the intruders from earth, which protects their interests for a little longer from the would-be colonists from Earth.
Yll from the story "Ylla" also kills Nathaniel York and men from the First Expedition, an action which benefits the martian populace by shielding them from colonization by earth men. Now Yll's motives may not have been completely well-meaning and for the good of the population; he really went hunting because he was extremely jealous of his wife's dreams. Nonetheless, his murder of the astronauts did benefit martian society as a whole.