Answer:
First of all we should know that the planets are in the orbit around the sun. Now, why does a planet orbit the Sun and not the Sun orbit the planet? The lighter object orbits the heavier one, so the Sun is heaviest one in the solar system. Moreover the Sun is 1000 times heavier than the largest planet, Jupiter.
Sir, Issac newton realized that the reason the planets orbits the sun related to why, objects fall to the earth when we drop something. The Sun's gravity pulls on the Earth, pulls down anything that is not held up by some other force and keeps everything on the ground.
Heavier objects produce large gravitational force than lighter planets. Therefore heavier planet in the universe is the Sun, produces strongest gravitational pull.