VGFacts

In Perfect Dark, during the "Duel" mission on Special Agent difficulty, Joanna is instructed to defeat Jonathan Dark.
In Perfect Dark Zero, Jonathan is introduced at the end of mission 7 after saving Joanna from Chandra Sekhar. In PD Zero, Jonathan's last name is Steinberg.
A few theories exist, or can be made, about why Jonathan's last name was changed:
* With Perfect Dark having been made before Perfect Dark Zero, Jonathan may have been Joanna's brother at one point in development
* It may have been a mistake in programming
* If Jonathan is Joanna's brother in Perfect Dark, with the mention of his last name as Dark only in the "Duel" mission on Special Agent difficulty, Jonathan was retconned and his last name was changed to Steinberg for Perfect Dark Zero
* Jonathan and Joanna married between Perfect Dark Zero and Perfect Dark and Jonathan took the surname of Dark

Catch Jonathan Dark's name in the first few seconds of the video


http://tvtropes.org/pmwiki/pmwiki.php/WMG/PerfectDark
http://www.gamefaqs.com/boards/960632-pe...k/53806204
http://www.gamefaqs.com/boards/516508-pe...o/48194165
http://perfectdark.retropixel.net/pd/guides/21.php
http://perfectdark.wikia.com/wiki/Jonathan_Steinberg
http://perfectdark.wikia.com/wiki/Joanna_Dark