Gemini is the third zodiac sign and its symbol is said to depict the twins Castor and Pollox. Those born under the Gemini sign between May 22 and June 21 tend to be charming and quick-witted with a tendency to be talkative, insightful and inquisitive. An air sign, Gemini’s ruling planet is Mercury and they are compatible with Aries, Aquarius, Libra and Leo.