Short answers, pulled from the story.
Alfred Marshall (the 26th of July 1842 - the 13th of July 1924) was an English economist whose 1890 textbook Principles of Economics dominated economic teaching in England for many years. He is called the father of scientific economics for synthesising supply, demand, marginal utility, and costs of production into the neoclassical framework that still underpins microeconomics.
Marshall invented the standard supply and demand diagram, developed the price elasticity of demand, defined consumer and producer surplus (sometimes called Marshallian surplus), classified costs into fixed and variable, and founded the Cambridge School of economics. He also helped develop the Cambridge equation in monetary theory alongside Pigou, Hawtrey, and Robertson.
Principles of Economics was first published in 1890. It appeared in eight editions, starting at 750 pages and growing to 870 pages, and decisively shaped the teaching of economics in English-speaking countries.
Marshall held academic posts at St John's College, Cambridge (fellow and lecturer from 1865), University College, Bristol (first principal, 1877-1881), Balliol College, Oxford (tutorial fellow, 1883), and finally Cambridge University, where he served as professor of political economy from 1885 until his retirement in 1908.
A Marshallian industrial district is a geographic cluster of small, specialised firms manufacturing related products, characteristic of late nineteenth-century Britain. Marshall described the concept in Book 4, Chapter 10 of Principles of Economics; its chief advantages are easy recruitment of skilled labour and rapid informal exchange of technical information, which reduce transaction costs to a practical minimum.
John Maynard Keynes and Arthur Cecil Pigou were among Marshall's most prominent Cambridge students. After Marshall's retirement in 1908, academic leadership of the Cambridge economists passed to Pigou and Keynes. Keynes also wrote Marshall's obituary, which Joseph Schumpeter called the most brilliant life of a man of science he had ever read.