The first labor theory of value quite literally comes from Adam Smith. It is integral to his ideas around the idea of the "Wealth of Nations".

To give quick and dirty summary that doesn't really get into the exact language he uses, but still gets the gist of the thing, basically, the economy of a state is fundamentally made up of two intertwining things. The wealth of individuals and the wealth of nations. The wealth of individuals can appear massive and sometimes appear to be the wealth of the state, with states with more rich people in them appearing to hold more power. However, these things are fundementally based on the wealth of nations. The wealth of nations refers to the actual capacity for economic and manufacturing improvement of a country. It's ability to use labor to make things and create meaningful capital improvements (or as Marx would later define, create labor value).

I will provide an easy example, the landlord. The landlord has the wealth of the individual and is incentivized to increase the wealth of his individual person. However, this incentive towards individual wealth does not mean that he is inherently incentivized to make meaningful capital improvements. He can increase his individual wealth by raising rent and never doing maintenance or improvements on the land. The wealth of nations is not built on this, but instead on creating capital improvements on the land, so it goes from a farm to a factory. That hands that were chopping wood instead dig coal, etc. That labor value increases.

Adam Smith basically says that the job of a state is to create the appropriate incentives to incentivize the creation of the wealth of the nation, not the creation of the wealth of the individual. Which people would know if they ever actually read Adam Smith and didn't just pretend to read him.

Ricardo and Marx take it a couple of steps further, with Ricardo explicitly defining that the wealth comes from the ability to marshall the labor, not actually from the capital improvement, and Marx redefining it as 'socially necessary labor' and investigating why such capital developments are piece-meal (the tendency of the rate of profit to fall which disincentives individuals and nations from pursuing capital improvements).

Thanks for the detailed explanation! I've never read Smith, never knew that the term "wealth of nations" was so... progressive and materialist?