Aries begins at the moment the Sun crosses the celestial equator going north — the March equinox. It is not merely the first sign by convention; it is the zero point from which every ecliptic longitude on every chart in this site is measured.
That makes it the definitional sign of the tropical zodiac. When a chart says a planet sits at 353°, it means 353° from the first degree of Aries, which is to say from the equinox itself.
Cardinal and fire: it opens a season, and it opens the one where daylight begins to win. The traditional attributions — initiative, impatience, the standing start — are the qualities of a beginning rather than of a person.
Traditionally attributed
Initiative, appetite, impatience, the appeal of a standing start.
Listed because it is what the tradition says, not because this site can check it. Everything above this line is geometry; everything in it is convention.