And also: we would have spaceships and nuclear blasters.
Seldon is the inventor of "psychohistory" - a kind of demography/political sociology/ group psychology on an interplanetary scale that can predict the broad sweep of history with amazing accuracy. Crunching the numbers shows him that the Empire is about to collapse and galactic society is about to fall into a dark ages that will last 30,000 years. However, Seldon has also figured out how to shorten that interregnum to 1,000 years via subtly planning out the course of the future, and establishes a foundation of scholars on a tiny planet out in the galactic boonies to carry out "the Seldon Plan".*
Overall Seldon is more of a mythic figure than a protagonist per se and he may be a bit of a trickster, as it becomes more and more clear that he arguably set up a double-blind experiment where the outcome is the fate of humanity and the confederates are hard to tell from the dupes. The series follows several centuries of the Plan, and if anyone can be said to be the hero of the story arc it's the Seldon Foundation itself. Over the course of the series, several forces arise to challenge the Foundation, and not all of them were predicted by Seldon.
Of the books, my favorite are those that cover the early leaders of the Foundation, as they resort to ever-sneakier and more inventive diplomacy to take on interplanetary warlords, the remnants of the dying Empire, and internal political intrigue. Asimov also does a nice job keeping the characters engaging, which is very necessesary when one of the basic conceits of your story is that the mass actions of humanity render their individual choices and actions more or less irrelevant.**
Plus, at the end of each crisis the Foundation faces, a little Hari Seldon hologram pops up in their town hall and explains how he'd had all of this predicted with an alpha = .05, given that he set up the Foundation when, where, and how he did. The series eventually starts to exhibit diminishing returns, but I think it stays pretty solid all the way up to Foundation's Edge.
If you like...
States and Social Revolution by Theda Skocpol,***
Guns, Germs, and Steel or Collapse by Jared Diamond,****
those old Star Trek episodes where Kirk and the gang find some planet run by a computer, or an alien dressed up like a 19th century dandy, or the Romans or something,
These books are for you.
*In regards to the amazing predictive power and causal heft of Seldon's Plan, he's also kind of the Golden Fleece of sociology as well, but that's neither here nor there.
**The duality of structure, determinism vs. agency - does this sound familiar to anyone else?
*** Come to think of it, given the logic of the plot, admirers of Barrington Moore might like it more.
****This Jared is not, FYI, the Subway guy.