The name Cassie is a diminutive form of the name Cassandra, which has its origins in Greek mythology and ancient Greek language. Cassandra was a daughter of King Priam and Queen Hecuba of Troy. According to Greek legend, Cassandra was blessed with the gift of prophecy by Apollo, but she later refused his romantic advances, which led him to curse her so that no one would believe her prophecies.

The name Cassandra is derived from the Greek word "kassandra," which is a combination of two words: "kekastai" meaning "to excel" or "to outshine" and "aner" meaning "man." Thus, the name Cassandra can be interpreted as "she who outshines men" or "the excellent one." The name Cassie emerged as a diminutive form of Cassandra, likely during the Middle Ages or Renaissance period in Europe.

One of the earliest recorded instances of the name Cassie can be found in the works of English playwright William Shakespeare. In his tragedy "Troilus and Cressida," written around 1602, Shakespeare introduces a character named Cressida, which is a variant spelling of Cassandra. Additionally, in his play "The Winter's Tale," written around 1611, Shakespeare includes a character named Cassandra.

Throughout history, several notable women have borne the name Cassie or its variants. For example, Cassia Longina (fl. 3rd century AD) was a renowned Roman philosopher and the wife of the philosopher Lucius Arrunitus Stella. Cassie Bernall (1981-1999) was an American student who was tragically killed in the Columbine High School massacre in 1999.

Other famous individuals with the name Cassie include Cassie Ventura (born 1986), an American singer and actress; Cassie Steele (born 1989), a Canadian actress and singer; and Cassie Campbell-Pascall (born 1973), a Canadian ice hockey player and two-time Olympic gold medalist.

The name Cassie has also been used in literature and popular culture. For instance, Cassie Blake is a fictional character and one of the main protagonists in the young adult book series "The Secret Circle" by L.J. Smith. Additionally, Cassie Ainsworth is a character in the popular British soap opera "Skins."