Why did Zelda become Sheik?

Sheik serves as Princess Zelda’s alter ego in the game; to escape Ganondorf’s capture, Zelda passes herself off as a male Sheikah known as Sheik. … Possibly owing to this, Sheik has become a popular character in The Legend of Zelda mythos, despite currently appearing only in one game out of the main series.

Who exactly is Sheik?

sheikh, also spelled sheik, shaikh, or shaykh, Arabic shaykh, Arabic title of respect dating from pre-Islamic antiquity; it strictly means a venerable man of more than 50 years of age.