Intellectual history for me is a composite of the thoughts of and actions of the many individuals who stood out by being outside the conventional mainstream. Those who were brave enough to challenge the ruling thoughts and theories of their time created the intellectual history.These are the men and women who changed life as it was known in their life time.
One can't think new thoughts without some sort of basis or framing for it. For example, the modern concept of "childhood" that we now take for granted -- the notion that children should lead safe, carefree, playful lives and be provided for and nurtured by and "enriched" by their parents, teachers, and by society is a very recent development. The lives of most children before the concept of childhood took hold were, by modern standards, fraught with abuse and neglect. Without the concept of "childhood" there were no child labor laws, no mandatory and free education, no priority placed on literacy regardless of social class, and marriages were early and rushed.
So meta-thinking about these things leads to what one might call thought-structures endorsed by society that brings about change. "Childhood" of course is just an example; attitudes toward a whole range of things like slavery / indentured servitude, the role of women, how to treat prisoners and the objectives of incarceration, and on and on, have been transformed by thinking about why things are as they are, how they could or ought to be, and how to make desired changes sustainable.
The word meta is used a lot to convey the idea of something going on at a level above the normal. Everybody knows that in a technical way, it usually means 'data about the data' like in HTML. So I see intellectualism in that way. The latest person in that category who I listen to is Jordon Peterson.