Marlo is a pre-war ghoul who was a war veteran who became a railway worker just before the bombs fell. He became depressed after losing all of his family with him not seeming to die from old age. He refuses to kill himself or let himself die due to his religious and moral beliefs. He's grumpy and tries to force anyone he meets away because he's afraid of them dying or having them outlive them. He believes he no longer has a purpose in this world, and only through the events of the game could you possibly give him this purpose.