Theodore Herman Albert Dreiser (August 27, 1871 – December 28, 1945) was an American novelist and journalist. He pioneered the naturalist school and is known for portraying characters whose value lies not in their moral code, but in their persistence against all obstacles, and literary situations that more closely resemble studies of nature than tales of choice and agency.

Dreiser's outstanding works were the novels Sister Carrie (1900) and An American Tragedy (1925).

Dreiser was born in Terre Haute, Indiana, to Sarah and John Paul Dreiser, a strict Catholic family. John Paul Dreiser was a German immigrant from Mayen in the Eifel region, and Sarah was from the Mennonite farming near Dayton, Ohio; she was disowned for marrying John and converting to Roman Catholicism. Theodore was the twelfth of thirteen children (the ninth of the ten surviving). The popular songwriter Paul Dresser (1857–1906) was his older brother.