Dr. Malthus, I Presume?
For me, though, Dr. Malthus is still king of the heap. His observation that the exponential character of reproduction could outpace any plausible increases in productivity is still the key to understanding relative economies. Indeed, many countries blessed with enormous wealth have seen the profits gobbled up by every increasing numbers of hungry mouths. The countries that have stayed rich for a long time all seem to have low fertility.
Such diverse countries as Vietnam, Bangladesh, Czechia and Cuba have all seen rather dramatic per capita economic growth in this century. What they have in common is very low or rapidly falling birthrates. No country better illustrates this than China, which adopted draconian measures to suppress reproduction and saw enormous dividends in economic growth. Sub-Saharan Africa is the opposite. Its nations are the world's poorest, and fertility rates are the highest.
Fortunately, draconian methods like those of China are rarely necessary. Simply educating women and providing them with birth control and other reproductive health services is the most effective method we know for decreasing fertility. Few women actually want to produce an endless stream of offspring that they can't afford to feed and educate.