In http://www.straightdope.com/mailbag/mdime.html,
BJJTshield asks whose face used to be on the dime
before the current [Roosevelt] dime, introduced in 1946.
The dime before 1946 was the Winged Liberty Head dime,
depicting a female head of Liberty wearing a winged
helmet. It was designed by sculptor Adolph A.
Weinman and introduced in 1915. Despite the obvious
femaleness of the depiction, the dime is widely referred
to as the Mercury dime, after the winged helmet of the
Roman god.
The allegorical figure of Liberty is historically the
most popular design for US coins. In fact, no US coin
depicted an actual person until the Lincoln penny was
introduced in 1909 for the 100th anniversary of Lincoln’s
birth.
Literally, however, the face is that of Elsie Kachel
Stevens, the young wife of poet Wallace Stevens. The
couple rented rooms from Weinman, who used a
bust of Elsie he made in 1913 as the model for the coin.
Source: http://www.coinworld.com/reading/collector/44wingeddimes.html