Fedora. It doesn't have to involve Indy at all but it could and the stories could range anywhere from the 1890s to the 1930s. I imagine him to be about Henry Jones, Jr.'s age (so born sometime in the 1870s.) Apparently, from the Holbein novels, Fedora is driven by a deep curiosity about the unexplained and his alliances are defined by money. I was thinking he would've grown up with a drunkard father and a kind but frail mother and that his desire to know the unexplained came from not only escapist leanings but also from a faith of sorts. He at once respects the unexplained but also wonders what benefit it could have for him, both financially and otherwise. He doesn't desire power though, and he's willing to work for anyone who would be willing to pay, regardless of politics or morals. He could be a drunk, as well, which would lead to him having an impoverised life which further neccessitated his greed. He would have perhaps a wife who died in childbirth (around the 1890s) along with the child, his son.
Fedora would be the "proto-Indy" (much like the heroes of the '30s serials, and like Secret of the Incas) and would as in his appearence in LC wear the Fedora, leather jacket and khakis. But his appearence would also appear less refined, older, and haggard, as would his clothing. He would be everything Indy is not and everything Indy is at the same time; He would represent that ''dark side'' of archaeology that Belloq spoke of. Whereas Indy was close to falling to the status of being a mere graverobber and mercenary for hire (he was always working for the greater good, in a sense, whereas Fedora would work for himself) but never did, Fedora would fall and this ''fall'' would come to define his life--Until he meets Indy, perhaps.
This could be a reason (besides Indy being so cunning) that he literally and symbollicaly passes the hat to Indy; Indy would remind him of the son he never came to know, and of himself. By being so obsessed with the unknown and greedy, he lost his family, and also himself, from which this dark identity of Fedora grew. He would never meet Indy again after the Cross of Coronado affair.
The incident in Utah in 1912 could in this way intertwine both Indy's destiny and Fedora's.
After this incident, Fedora stops being a grave robber (He has no illusions about nor objection to grave robbing, whereas Indy would later on) for some time or even permanently, realizing that he was once like the kid (Indy);Respectful of the unknown, and of the artifacts which represent that unknown and also realizing how far he had fallen. Look at the way he stares at the Cross when he firsts recovers it--there is a sense of wonder in his eyes
http://www.theraider.net/showimage..../films/crusade/gallery/dvdscreenshots/007.jpg--but that wonder is quickly absorbed by greed, until he meets Indy. In passing the fedora to Indy, the identity of "Fedora"--the graverobbing, greedy one, might pass away, only to to be replaced by a repetant one. Or it could go another way.
This I'm not sure of, but Abner might've been a competitor of his, but Indy would never know about it. I was thinking Fedora, like Abner could be could either fascinated with the Lost Ark (considering it the summit of all power and a way to truly understand God; like the Grail it would be a way to access the divine and thus understand more about himself. Searching for it would lead to direct competition with Abner and Fedora's demise at Abner's hands) or the Greek Tablets of Destiny (Because the idea of them fascinate them; or he could've been hired by some one to find them and only becomes fascinated with them after learning more about them) or the Tree of Life (for knowledge and a way to absolve himself of his alcoholism; a cure.)
I'm also not sure if Half Breed, Roscoe, and Rough Rider (his associates in LC) would be his friends or simply other mercenaries that he hired. They seem to have a familiriety with him, implying they've worked together before. Rough Rider is described in the LC script as a bowery boy of 14 and a bully. Either way, these characters would be much darker and grittier than Indy, drunkards and scum. Fedora would be the same, in some ways, but would also have redeeming qualities.
There are multiple ways it could go.