Playing Hari Seldon in Foundation series.

[With a box]

I know he was dead before story starts.
The PC I will play would near epic (18th) wizard.
(I want advises about class, but I don't think that anything other then T1 caster can do this.)

He predicted entire plot and left note about it.(and dead) and make a gulid of mages to perform them.

Problem is, if I do this straightforward I need to outsmart everybody and make prophecy of them, witch is not possible.

What should I do to make this concept playable?

[Snowbluff]

Well, a heavy divination focus would be good. I'm not sure "prophecy" is a good word for what he ended up doing. More like societal engineering.

What system are you playing? There are some thematic feats for either version. Sacred Geometry for PF, Knowledge Devotion for 3.5.

A hefty sense motive would be useful as well. Additionally, I think there was an optimization method that let you know EVERYTHING. Finally, a wizard that high of a level can Teleport Through Time, which is handy for double checking your work.

[Red Fel]

First off, I don't see Seldon as a Wizard. Wizards aren't just smart; they are applied, weaponized smart. They bend reality with their brains.

Seldon didn't do that. Seldon wasn't like that. Seldon was a psychologist and mathematician. Seldon's whole schtick was his ability to use mathematical formulae to represent, and to predict, human behavior in the aggregate (quintillions of people make for a lot of statistical significance). I could see Seldon as a class like Factotum, or frankly even Expert, with max ranks in Profession (Psychohistorian).

Because, here's the thing - apart from organizing and motivating people and plots, and compiling the Prime Radiant, Seldon didn't actually do anything. He set up a course of events with knowledge of a highly probable outcome, and tasked groups with ensuring that the outcome remained highly probable. Any number of class features - spells, sneak attacks, feats - don't apply, because he didn't use them. He used his brains.

Which leads me to my second point: I don't see Seldon as playable. Not as a PC, not as an NPC, and here's why.

As a PC, Seldon would be able to predict - through calculation - major world events, at best. It is repeatedly noted that the actions of individuals are beyond his mathematical abilities to foresee. So he can't predict the actions of individuals, which is really the vital skill for a PC in his position. So he's somewhat useless. Alternatively, if you say he can predict individual actions, you are jeopardizing player agency. What happens, for instance, if you predict that the party Rogue will choose stealing the idol over saving his friends? Has the player's choice been made for him, now?

As an NPC, you face the same problems, with a greater emphasis on the second. The fact is that Hari Seldon was an infuriating character in the books, because you would look back at him through the lens of history and he'd still be sitting in that chair, book on his lap, fingers steepled, with an "I have foreseen this" smirk on his face. He was insufferable in that respect, and the reverence that people had for his foresight bordered on (and on some planets, rose to the level of) deity worship. A Hari Seldon NPC would be presented as an irritatingly all-knowing oracle, revered for nigh-omniscience, yet who could never make his predictions known until after they came true.

Your PCs would want to kill him.

But again, player agency is an issue. A Hari Seldon can't predict the actions of a handful of PCs. And even if he could, it wouldn't last. Have you read all three books? By the third, everyone is straining against Seldon's plan, struggling with it. Imagine what the PCs could do if they caught wiff of a prophecy involving them. You couldn't stop them from wrecking it. It would be instinct for them.

[Ashtagon]

Which Hari Seldon?

Hari Seldon the parkour expert and dirty fighter?

First Minister Hari Seldon?

Hari seldon the mathematician?

I'd build him with a mix of rogue/swashbuckler/scout (for the parkour stuff), aristocrat/noble (for the first minister) and either expert if playing the maths low-key, or some kind of divination trope if playing it high-key. If high-key, his powers should be chosen based on the idea of divination only reliably working on groups (preferably large groups) -- certainly, nothing that relates to enhanced senses.

[Zubrowka74]

I think he's more of a plot item than a PC or NPC. What you could do, though, would be a PC dedicated to his philosophy. A priest worshipping a philosophy, if your DM agrees to allow this.

[Vhaidara]

The best way I can think to reproduce that kind of effect would be optimizing Knowledge (History) and abusing the bit where you can know the date of an event through Knowledge (History), but it never specifies that the event must be in the past. That's basically what he did: He knew when things would happen because of his knowledge of history (and the patterns therein).