The sub-atomic world of Bast, ravaged by a nuclear holocaust, needed new sources of power to survive. Thus, the conniving Jarr sends his creation -- the Cyborg Sinister -- to Earth, specifically Stark Industries, to seek out these needed power sources. It is revealed by Jarr's cousin, Tyrr, that the Cyborg Sinister is actually the "gene twisted" AIM-created Adaptoid which Jarr had sent to Earth! Whoa! Iron Man gives the obligatory battle, and finds the C.S. to be a pretty tough foe! The two go at it for awhile, then IM dumps a vat of corrosive chemicals on the cyborg. Still not out, IM pounds on C.S. some more until Jarr decides to activate a self-destruct circuit on the C.S.! But cousin Tyrr won't let him, and thus the Cyborg Sinister lies defeated -- and in pieces -- on the floor of an S.I. lab.

In Captain Marvel #50 (original series), the first 5 pages is all Iron Man vs. the Adaptoid. We now find out that the acidic remains of the Cyborg Sinister were put into a holding tank for future study, and after an explosion (during the scuffle with the Controller in IM #91), a crack formed in the tank and the now-liquid remains of the 'borg oozed out to once again retake the form of the Adaptoid!  He eventually hid around Stark enterprises for a bit, adapting various personnel, until he viewed IM in action and took his form (appearing as the classic Iron Man, albeit green with no mouth slit; in fact, it's when IM is testing a new invention of his, the huge JUPITER LANDING vehicle (precursor to the Layton/Michelinie 'lander?). The Adaptoid attacks, and at first IM thinks someone stole one of his armors!  They go at it, until the Adaptoid grabs and hurls the lander at some hapless employees to keep IM busy so he can escape.  IM radios the Avengers, as the Adaptoid goes there to attack, and in the end (being it's Capt. Marvel's mag), he is tricked into absorbing Capt. Marvel's powers, and Marv makes the Adaptoid accidentally hit his nega-bands together, sending him into limbo and releasing Rick Jones.

First ever & IM appearance: Iron Man #51.
(Special thanks to HUGO NEGRON for his additional information!)