Gemini (Gem-en-i.e.) is the third astrological sign in the Zodiac, originating from the constellation of Gemini. In astrology, Gemini is considered a "masculine", positive (extrovert) sign. It is also considered an air sign, and is one of four mutable signs. In astrology, a planet's domicile is the zodiac sign over which it has rulership. The planet said to be ruler of Gemini, or those associated with Gemineans, is Mercury.