Final answer:
Cassio's rank before being demoted by Othello is lieutenant, which plays a crucial role in the developments and tragedies in Shakespeare's play, Othello.
Step-by-step explanation:
The rank that Cassio holds before Othello strips it from him is that of lieutenant. Cassio's demotion is a pivotal moment in William Shakespeare's play, Othello, and it sets in motion a series of tragic events manipulated by Iago, which ultimately lead to the downfall of several characters, including Othello himself. The removal of Cassio's rank not only affects his military career but also contributes to the tragic narrative and the complex interplay of loyalty, honor, and jealousy explored within the play.