Mooltrikona sign is another very important and interesting concept of Vedic astrology to understand before reading the kundli. Mooltrikona sign is the second power placement of the planet in the kundli after exaltation sign. Which means if there is no planet in the exalted state in the chart then look for the placement of planets in the mooltrikona sign which is considered very good and then look for the planets in its own house.
Mooltrikona sign is where planets are most comfortable and feels really at home thus producing the better results even than exalted sign. Most of the planets own two signs, out of these two one is their mooltrikona sign based on the fact that they share almost similar feature. For example, Mars rules Aries and Scorpio. Mars represents will power, courage and action. Aries represents active and go-getter kind of people closer to Mars characteristics. Hence, Aries is Mool Trikona sign of Mars. Scorpio will still be called its own sign.
Following chart will help you to understand it in a better way.
When we check the lord of ascendant in kundli, the lord of the ascendant would be applicable only to those ascendants which contain mooltrikona sign of a planet. The placement of a planet in a particular house links the significations of its mooltrikona house with the significations of its house of placement. Not only this, when we consult the divisional charts, we look at the Mooltrikona sign lord of the concerned divisional chart ascendant. For example for analysing professional matters the mooltrikona sign lord of the ascendant of Dasamsa becomes additional prime determinant. Further, while analyzing the dasha-sub-dasha (main period-sub period), we identify the house where the mooltrikona sign of the sub-period lord is placed and the natal/ transit houses occupied by the sub-period lord.