The link between descriptive and substantive representation is well established in the literature but is hard to trace historically, where class records are thin. We introduce a replicable enduring-elite surname measure, pairing a contemporary socioeconomic criterion with historical elite registers, and apply it across the Chilean Congress, 1834-2020. Against a dynamic population reference built from 22.65 million birth registrations, the enduring-elite share of Congress falls from about half in the 1860s to about 12% in the 2010s, with a sharp drop of 11 to 13 points around the 1925 constitutional reform. In 1910-1950, composition co-moves with the legislative agenda, net of party: common-surname legislators emphasize labor foremost, elite legislators a statecraft agenda of defense, foreign affairs, and administration. Across this window, who sits in Congress moves together with what Congress attends to.