6. John Marston
Rockstar included a number of Red Dead Redemption nods in Grand Theft Auto V, from the book titled Red Dead by J. Marston that can be found in Franklin's second safe house through to the geographical reference points such as road names and a very familiar looking farm, and the most blatant (though obscure to find) comes in GTA Online. If you head into your character generation screen and spend some time fiddling around with your lineage - specifically by repeatedly hitting the randomise character option until Marston appears as your father. It's not actually possible to select Marston by scrolling through the parentage options, no matter how committed you are - he's merely a reward for anyone who hammers the randomise button a few times.
How To Find Him Within the character customisation menus in GTA Online, hit random character repeatedly and eventually the Red Dead hero will appear as your father.