English term for pre-thinker?

I was searching for an English translation for the German Vordenker. Basically a person, often a scientist, who began or further significantly developed a new concept or theory by contributing epoch-making publications or comments. Translation services give out expressions that have more the connotation of thinking about actual future events or things to me, e.g. innovative business ideas/products or future studies. But Vordenker doesn’t imply thinking of future actually, rather new ideas outside of current paradigms. Also Vordenker is in my opinion especially used in a historical or biographical context, as you can only judge his influence retrospectively (e.g. times cited). A lot of scientists in German wikipedia are described as Vordenker in the first sentence while there seems to be no common english term in the english wikipedia.

Thought leader has a too imperative character.

Forward thinker implies to me thinking of future itself.

Key figure is too inexact.

Visionary means someone with new ideas, which possibly never have come true in retrospect.

Pre-thinker sounds like awkward & uncommon English. Is there a better known expression? Or what would be a good one regarding above constraints?

Update: See how german.SE thinks about appropriate synonyms

https://german.stackexchange.com/questions/2337/whats-a-synonym-next-to-vordenker-vorreiter-freidenker-pionier/2344#2344

Pioneer (often seen in adjectival form, as in "a pioneering scientist") is a reasonably close match.

But I doubt you'll find an exact analogue. A pioneer or a trailblazer does something first, and a visionary thinks something first, but I don't think we have a common word for someone who thinks and does something first, or someone who does something thought-related first. (In point of fact, when English lacks a perfect word for a useful concept, we often end up importing one from German: zeitgeist, schadenfreude, etc. Maybe we should start using vordenker!)

It sounds like you are looking for a word to describe a person who possesses foresight and intelligence.

With that in mind, you might look at mastermind:

mastermind |ˈmastərˌmīnd|
noun
a person with an outstanding intellect: an eminent musical mastermind. • someone who plans and directs an ingenious and complex scheme or enterprise: the mastermind behind the project.

Still, don't toss visionary on the scrap heap too quickly:

visionary |ˈviZHəˌnerē|
noun ( pl. visionaries )
a person with original ideas about what the future will or could be like.

Usually the latter term is applied to people who were successful in grasping possibilities and bringing them to fruition.

The terms freethinker and trailblazer are excellent here.

Freethinker:

a person who forms opinions on the basis of reason, independent of authority or tradition, especially a person whose religious opinions differ from established belief.

Trailblazer:

2. a pioneer in any field of endeavor: a trailblazer in science.

Both of these, especially trailblazers, are often not recognized as such during their trailblazing activities; many times only in retrospect do people recognize the value of their contributions.

Edit: I didn't do a thesaurus search, and therefore missed the word pioneer. Suggested by @phenry, I have to say I cast my vote to that one. Pioneer or pioneering is best.