No. Not anymore. A Superman must not kill. I learned it the hard way. 
- — Superman
Action Comics #644 is an issue of the series Action Comics (Volume 1) with a cover date of August, 1989.
Synopsis for "Doppelganger"
Superman heads back to Smallville to check on Matrix, only to end up in a fight with him. Lana, Jonathan, and Martha Kent try to convince Matrix that he is someone else. Matrix finally realizes he is dangerous, and, just like Superman, exiles himself from Earth to avoid putting anyone in jeopardy.
Appearing in "Doppelganger"
Featured Characters:
- Superman (Flashback and main story)
Supporting Characters:
- Jonathan Kent (Flashback and main story)
- Lana Lang (Flashback and main story)
- Martha Kent (Flashback and main story)
Antagonists:
- Matrix (Flashback and main story)
Other Characters:
Locations:
- Arizona
- Metropolis
- Smallville (Flashback and main story)
Items:
Vehicles:
Notes
- This issue is reprinted in Superman in the Eighties, Superman: The Exile & Other Stories Omnibus and in Adventures of Superman: George Pérez.