Vera Brittain (died 29 March 1970)
I discovered Vera Brittain through the remarkable 1979 BBC dramatization of Testament of Youth, the first volume of her memoir, originally published in 1933. (The second volume, Testament of Experience, was published in 1957).
Born in 1893, Brittain became a nurse, a writer, a peace activist, and a pacifist. I found reading her Testament of Youth a transformative experience--it details Brittain's struggle for an education, her experiences at Somerville College (Oxford) in 1913, the devastating impact of the war that began in 1914, her experiences as a nurse during the war, and the consequences of war not only on the lives of the men who fought and died but also on the lives of women--the mothers, sisters, wives, daughters, and lovers of those men. (Testament of Youth covers the years 1900 to 1920.)
There's an excellent online biography here. There is also an excellent full-length biography, Paul Berry's Vera Brittain: A Life. But why not start with Bittain's own account of her life, Testament of Youth--you will never forget it.
(And, by the way, on the occasion of the one-hundredth anniversary commemoration of the beginning of World War I, the BBC produced a new film version of Testament of Youth.)