Who are Wilfred Owen and Siegfried Sassoon and why are they associated with World War 1?

They are two of the best known "War Poets" they wrote some powerful poetry about life in the trenches during WW1 which had a lasting cultural effect.

"Dulce Et Decorum Est" is probably the best known by Owen and

"Counter Attack" is probably Sassoon's

Go read - they are all over the web and both are short.

Owen was killed very near the end of the war.