The lord of 1st house is also known as the Ascendant lord or the ruler of the Ascendant. The Ascendant, or the rising Sign, is the zodiac sign rising on the eastern horizon at the time of a person's birth. The planet that rules the zodiac sign on the cusp of the first house becomes the lord of the first house. So, for example, if the first house cusp is in Aries, Mars, the ruler of Aries, becomes the lord of the first house.