Doubtwalker is a short story that was released in 2012. It corresponded to something Blizzard was doing in the days before Diablo III was released. You can read Doubtwalker online (and download it as a PDF).
The Witch Doctor was the fourth Diablo III character to be revealed in the days before the release of the game. Blizzard had a “Gathering of the Heroes” page (which has since been taken down) where players could watch a class video, and learn about the skills, resources, armor, and weapons that connected to a specific class. In addition, there was an exclusive short story about each class.
Today, that same information can be found as part of the Game Guide in the Diablo III section of Battle.net. There is a link to the Doubtwalker short story on the Witch Doctor class page in the Game Guide.
Doubtwalker is the story of Benu, a witch doctor from the Clan of the Seven Stones. He has embarked upon his first Igani Bawe (also called Harvest of Souls). It is a ritual war where witch doctors of each Clan hunt the others, take captives, and sacrifice them.
Benu had been taught that the spirits themselves are the ones who call for the Igani Bawe (which typically happens at the change of seasons). Those who took captives earned praise and admiration from the other members of their Clan.
Benu, and everyone else in the various witch doctor clans, had been taught that being offered as a sacrifice to the spirits was an honor. The person is released from this world – the shadow world – and able to enter the Mbuiru Eikura (also called the Unformed Land).
Something unexpected happened during the Igani Bawe that leaves Benu questioning the beliefs that he has followed all of his life, as well as the motives of the elders who initiate the Igani Bawe. He is compelled to find out what the truth is.
Those of you who enjoy playing a Witch Doctor in Diablo III should read this story. It gives you a look into the beliefs of the witch doctors, and it provides more explanation about how some of the skills in the game work. Have you ever wondered why the zombie dogs have bodies that look human (instead of canine)? It is explained in Doubtwalker.