There are specific theories of history that hold that 'primitive peoples' are merely in early stages of evolution, essentially 'behind' us, waiting to catch up. These theories tend to superimpose time periods such as 'renaissance' and 'modernity' onto other cultures; as though every culture were moving in the same direction, and those primitive cultures are merely backwards/behind rather than genuinely different.
I cannot for the life of me remember who the main theorists behind this are, or what a collective name for this theory of civilization might be. (Maybe Benedict Anderson, Freud, even Berkeley, some part of the 'westward course of civilization theory?)
Could anyone help enlighten me?
This question stands at the intersection of history and anthropology. In the study of culture this is often the case.
Though the term "primitive" is now rejected entirely in anthropology, it was used freely through the nineteenth century to describe a wide range of peoples across the globe. This was part of the unilineal cultural evolution theory.
There are many degrees of unilineal cultural evolution theory, which itself has changed dramatically over the last century, an in its current form is the subject of debate. But more directly related to your question of the past, the best example of the free use of "primitive" and "savage" is the work of Lewis Henry Morgan, who wrote quite a bit on the Iroquois Confederacy in the latter half of the nineteenth century. In his monumentally important (though now largely rejected) Ancient Societies, he argued that culture went through three stages: savagery, barbarism, and finally civilization. Though a useful model for classifying cultures, it is a very narrow understanding.
Indeed, the name "unilineal" suggests a single progressive line, ignoring the fact that cultures could exist in between these arbitrary categories. Further, a culture could and did suddenly jump up through the categories, essentially skipping steps toward "civilization" that were thought to be predetermined. At that, it suggests that those societies classified as "civilized" (almost exclusively European cultures) are at the top of a hierarchy of culture, suggesting competition or dominance in situations where neither is appropriately applied.
Morgan is just one example, but he's a very apt one, and was very influential. I do still recommend reading Ancient Societies, just doing so critically.
This isn't so much a single theory as an attitude with a very long history, manifested in multiple specific theories, and it's still around today in various, quite popular forms. The idea, in it's most broad sense, is 'the idea of progress'.
The most extreme form of this, the one I suspect you're interested in, is the idea of social evolution, espoused by a lot of early sociologists. Auguste Comte's 'three stages' are a good example of this, along with Durkheim's forms of solidarity and the work of Herbert Spencer.
These theories aren't exactly what you're describing though, because what you're describing is an attitude derived from an intellectual climate similar to the one that produced those theories. The idea that history 'progresses', although it has been under heavy, convincing criticism since WWII, is still popular today, however. Weber has a similar theory to the ones above in his classification of types of authority and his ideas of modernity. However, his ideas directly influence the later ideas used to criticize the whole idea of progress. Your question itself is problematic because it's easy to say that someone like Habermas, who would never use the term 'savage', is part of that continuity of thinkers who believe in sociocultural progress.