This is not a doctrine of the church, but a piece of folklore. The origin of it is to be found in Abraham Smoot's account of how David Patten, an early member of the church, claimed that in 1835 he was riding along on his mule when he was approached by a very tall man, dark of hue and covered in hair. This person identified himself as Cain. He was wandering and longed for death.
Some Mormons have identified this person as Bigfoot and thus this curious legend has grown up.
|Image courtesy Lon Strickler|