The Bikura are a tribe of seventy seedship survivors who crash-landed on Hyperion many centuries before the beginning of Hyperion. They all carry a Cruciform parasite which has kept them alive over the centuries, but as a result of the imperfect nature of the Cruciform's resurrection they have all become bald, neutered, mentally stunted dwarves. They are described as having facial features that recall the genetic defects associated with Down's Syndrome.
Father Paul Duré encounters the Bikura according to his journal as read by Lenar Hoyt prior to the Final Shrike Pilgrimage. He finds them living in a crude village at the edge of the landmass that gives way to the Cleft. They speak a corrupted, extremely simplified version of early Web English. The priest must use an interpreting device while communicating with them.
The indigenies do not call each other by any names. Father Duré gives somes of the Bikura "names": Alpha, Beta ("Betty"), Delta, among others. Although the Bikura are sexless, Duré gets a sense of "gender" from them, and has the impression that Alpha is "male" while Beta would be a "female"
The Bikura are hunter-gatherers with virtually no technology of their own. Their diet consists primarily of Chalma tubers and berries, as well as dead Arboreals (presumably descendants of Old Earth primates) that happen to fall from trees, though they do no hunting of their own. They live in simple shacks made of vegetable matter and crude materials. They wear simple rough woven brown robes, and have a strong tabboo against nudity.
The natives call themselves the "Three Score and Ten", an allusion to the number of their population (70) individuals. They seem to follow a type of memorized religion, calling themselves "of the Cruciform", and worshipping "in the room" (the Basilica in the Cleft). They immediately murder anyone who is not "of the Cruciform". They initially think Duré is "of the Cruciform", but once they realize that what he wears is instead a crucifix, they attempt to kill him. Alpha, however, intervenes. After "deliberation", the Bikura allow the priest to become "of the Cruciform" - by taking him down to the entrance to Hyperion's labyrinth, where the Shrike makes an appearance. The walls of the entrance are covered in cruciforms of all sizes. They collect one and hang it around the Father's neck, which, unbeknownst to him, would grow into him and become an part of his own body.
Duré eventually discovers the nature of their immortality -- the Cruciform -- but not before being bonded to the parasite himself. At the end of the Hoyt's tale, the Bikura and their village are wiped out via nuclear charges. Whether any of them survive via resurrection from the Cruciform is never stated, and it assumed they all suffered the "true death."