Short answers, pulled from the story.
Malthus argued that population grows exponentially while food production grows arithmetically, meaning any improvement in living conditions temporarily raises wellbeing but inevitably leads to population growth that cancels the gain. He described this as the Malthusian trap. The theory appeared in his 1798 book An Essay on the Principle of Population.
Thomas Robert Malthus was born on the 13th or the 14th of February 1766 at The Rookery, a small mansion near Dorking in Surrey, England. He was the sixth of seven children of Daniel Malthus and Henrietta Catherine.
Malthus identified two categories: positive checks, which raise the death rate and include hunger, disease, and war; and preventive checks, which lower the birth rate and include birth control, postponement of marriage, and celibacy. He favored preventive checks, particularly later marriages, as the means to maintain a higher standard of living.
From 1805, Malthus was Professor of History and Political Economy at the East India Company College in Hertfordshire. His students there nicknamed him "Pop", "Population", or "web-toe" Malthus.
Charles Darwin and Alfred Russel Wallace, the pioneers of evolutionary biology, both read Malthus. His framework of population pressure against limited resources provided a conceptual basis that influenced their thinking about competition and natural selection.
Ebenezer Scrooge's line in A Christmas Carol about the poor decreasing "the surplus population" is a direct Malthusian reference. Aldous Huxley named a contraceptive device the "Malthusian belt" in Brave New World. The villain Thanos in Avengers: Infinity War is widely read as Malthusian, and the musical Urinetown ends with the cast declaring "Hail Malthus!"