: They look vaguely human, and I guess the Pfhor could have taken some captives
: from Tau Ceti when they returned. But is this confirmed by a canon source?
http://marathon.bungie.org/story/scrapbook.html#nueveback is Rob McLees' relevant bit in the Scrapbook. From there:
Rob wasn’t content to simply revise older aliens; he created several new ones as well. One such creation was the “cyborg tank” with its Michael Jordanesque weaponry - the bouncing bomb. These were originally conceived as surgically-altered Bobs, an “enemy” the player might feel bad about killing. (Then again, some people like to kill Bobs.) Rob explains how the idea arose:
“Remember after you and Durandal hoofed it away from Tau Ceti, the larger force of Pfhor show up and rain on everybody’s parade Being slavers they grab up what they can and turn the rest into sub-atomic salsa. [sic] Well I initially put forward the idea that you might run across these loin cloth-wearing shackled Bob’s on one of the Pfhor ships (and at several locations planetside), but no one would go for it... so then I came up with the idea that the Pfhor have all this information on you from tapping into the information stored in the ‘Pattern Buffer Devices’ that you dumped your ‘pattern’ into all over the Marathon. So the Pfhor have a bunch of schematics and all this raw material but no experience this sort of advanced surgery and only 17 years to ‘get it right’. So basically the ‘cyborg tanks’ are these unfortunate Bobs that have been ‘radically, surgically altered’ so that the Pfhor would have some hard guys of their own waiting for you when you got to Lh’owon! Of course none of this ever made it into the game.”
Dunno whether or not that qualifies the "cyborgs as altered BOBs" idea as official canon, but that's as close as you come to their origins (so far as my quick searches found; there should probably be a question mark in the middle of that first sentence of McLees explanation). In M2, though, Blake does mention them on KYT:
The Pfhor have traced our communications
and our base is under attack by their
cyborg slaves who are immune to the ancient
S'pht virus. We're retreating deeper
underground now.
If the cyborgs are "cyborg slaves", then they're certainly biological; if the S'pht virus doesn't affect them, they aren't the type of Pfhor that the S'pht have fought before. So the cyborgs are a recent addition to the Pfhor clientele (as it were), and so Rob McLees' stuff could still be accurate even though it's never stated in any of the games.
Beyond all this, I couldn't tell you.
Lunair
