Cassandra

 and its variant Cassie appears several times in the Doctor Who universe and the related real world. They are listed below in alphabetical order by surname. If no surname is available, alphabetization occurs by the disambiguation term — that is, the bit between the parentheses in a title like Waitress (Random Shoes).

As only name

 * Cassandra (Annihilation), a Time Lord (AUDIO: Annihilation)
 * Cassandra (Asylum of the Daleks), a Dalek puppet (TV: Asylum of the Daleks)
 * Cassandra (The Myth Makers) the Greek prophetess (TV: The Myth Makers)
 * Cassandra (The Scarlet Empress), a Scarlet Empress of Hyspero. (PROSE: The Scarlet Empress)
 * Cassandra (Who Killed Kennedy), an alias for a whistleblower (PROSE: Who Killed Kennedy)
 * Cassandra (Zagreus), a Sister of Karn in the time of Rassilon (AUDIO: Zagreus)

As first name

 * Lady Cassandra O'Brien.Δ17, the last known "pure" human inhabitant of Earth prior to its destruction (TV: The End of the World, New Earth)
 * Cassie Rice (TV: Dreamland)
 * Cassie Scholefield (AUDIO: Project: Twilight, AUDIO: Project: Lazarus)

As name of object, publication or other in-universe item

 * Cassandra (ship), a sailing ship (AUDIO: The Secret of Cassandra)
 * Cassandra (So Vile a Sin), the outermost body orbiting Agamemnon, in reality a TARDIS damaged ten million years before (PROSE: So Vile a Sin)

Extra

 * Cassandra (actress), who played a Movellan Guard in TV: Destiny of the Daleks.

Audio

 * The Secret of Cassandra, a Bernice Summerfield audio drama.