Karaka means indicator, to make or do, to produce or create, and also
that which is instrumental in bringing about an action. The Atma Karaka planet, or soul planet, is the one that you have the most karma to work with in this life. It is the most important karaka.
This AK planet is the key that controls all other factors, elements and significations of the chart, as a king influences the affairs of its subjects and its lands.
The natural significations of the planet will share a lot about what you are working on in this life time, what is most alive in your personal mythology, and what karmas are an intimate part of your work. The work of the Atma Karaka planet is work that is being done on the soul level of life, the Atma. How the AK planet interacts with the rest of the chart will also share how your soul responds to life, your environment, and ultimately others.