Development Gag: Galen Marek's code name "Starkiller" was Luke's surname in the prototypical Star Wars; which George Lucas changed at the last minute.
Franchise Killer: The second game's disappointing numbers (combined with the closing of LucasArts three years later in 2013) killed the possibility of a third game, and Starkiller's adventures were Left Hanging.
PROXY would have been a "Corpse droid" where he often harvested organs to complete himself. However, because of his not fitting in with the team dynamic, and more obviously because the only way to give a comical aspect to him (grafting organs into himself) was considered too gruesome for what was intended to be a "T" rated game, he was redesigned to be a holodroid.
Before creating the character of Rahm Kota, the makers wanted Starkiller's Jedi mentor to be the Force Ghost of either Qui-Gon Jinn or a reformed Darth Plagueis.
Starkiller could have been called "Darth Icky" or "Darth Insanius" via official mandate from George Lucas. No, really.