So I've heard some reports of the Wachowski's logic for the way Hanks was cast, and I actually quite like it though I don't think I would have ever figured it out.
The echo of Hanks character through history is a fairly terrible person in almost all of the stories.
The poisonous Dr. on the boat, the Cockney brawler even when he's just playing the front desk worker in the hotel in the Frobisher story he acts only to fulfill his covetous nature.
In the 70s story he's playing a scientist who is doing some work for some fairly greedy evil people who want to purposely cause a nuclear accident. He knows this is the case, but was getting ready to pick up and leave without doing anything about it.
Until he meets Halle Berry. As he describes, he feels a connection to her that he can't explain. She inspires him to help her take action against the conspiring company. Unfortunately, the company has him killed shortly after.
In the 2012 story line, Hanks character, having never crossed paths with an iteration of Halle Berry, is back to being a crappy self centered person.
In the final story line, 100 winters after the fall, the echo of Hanks has been through a journey rather than just being reiterated in each life. There has been some change, possibly linked with the brief connections with Halle Berry. He is no longer the manipulating lunacy of the 19th century ships doctor. He is still quite conflicted, struggling with the darker, self centered and self doubting aspect of himself. This aspect is personified by the weird Hugo Weaving imp.
Hanks once again meets Barry and in this life, they are able to make a stronger connection and the interaction allows Hanks to finally overcome the struggle with the darker parts of his soul.