c. 1300, originally comparative of up (adj.). Similar formation in Middle Dutch upper, Dutch opper, Low German upper, Norwegian yppare. Upper hand "advantage" is late 15c., perhaps from wrestling (get the over-hand in the same sense is from early 14c.). Upperclassman is recorded from 1871.
Upper crust is attested from mid-15c. in reference to the top crust of a loaf of bread, 1836 in reference to society. Upper middle class (adj.) is recorded from 1835. Upper ten thousand (1844) was common mid-19c. for "wealthier and more aristocratic part of a large community;" hence uppertendom.