Walter Cuthbert Blythe is the second child and son of Anne and Gilbert Blythe, named for Anne's dead father Walter Shirley, and her adoptive "parents", Matthew and Marilla Cuthbert. He is, by far, the handsomest of the six Blythe children, with wavy, black hair and dreamy grey eyes. But, he is said to be "step out of kith and kin", because he resembles none of his living relatives.
In Rainbow Valley, it indicates that he already has a love for words, and he is another of Anne's children who inherits their mother's imagination. He is the one who names Rainbow Valley in the first place, as well as the White Lady (a large tree that blossoms white flowers in spring) and the Tree Lovers (two trees whose trunks lean together and boughs are entwined). Walter takes a certain "Uncle" Paul Irving, who is a famous poet who started of as an Avonlea schoolboy, as his role model, and eventually manages to get a few of his poems published, including his "Sonnets To Rosamond" aka Faith Meredith, who he has a childhood passion for. Then, in Rilla of Ingleside, after the Great War breaks out, he writes a poem called "The Piper", about how the Piper calls young men from all over the world to fight, and they have to follow no matter what happens. He becomes truly famous, and his poem is printed everywhere, and recited many a time to the soldiers who are being seen off.
Eventually, though he shirks it for a long time, using the fact of his recent case of typhoid fever as an excuse, he does enlist, himself, to go and fight. I am not a spoiler, but I copied this line from Anne of Ingleside.
SPOILERS! READ AT YOUR OWN RISK!
Walter was smiling in his sleep as someone who knew a charming secret. The moon was shining on his pillow through the bars of the leaded window ... casting the shadow of a clearly defined cross on the wall above his head. In long after years Anne was to remember that and wonder if it were an omen of Courcelette ... of a cross-marked grave "somewhere in France."