In every game, except this one, Johnny Gat seems to almost die. In Saints Row, it was him being kidnapped. In Saints Row 2, he gets stabbed. In Saints Row 3, he gets stabbed again, also accompanied by supposedly being "officially" dead which is proven to be untrue in Saints Row 4.
Johnny Gat is the only character that appears in every game besides The Boss.
The Boss appears as however they were created (gender, race, voice) in Saints Row IV.
This is the first game where Johnny Gat and Kinzie are playable characters.
This is the first game in the series where the boss isn't a playable character