The word graha and planet are somewhat different. Planet means a spherical body orbiting around a star or a black hole whereas graha (a Sanskrit term) means an entity in the sky (with its own characteristics) that can seize, grasp, control, hold or influence you. In other words grahas are the celestial entities moving around the sky day and night to influence us through time. This includes Sun, Moon and all the planets in the Solar system. We are here because of them so we are always influenced by them 24x7.
Vedic astrology has a total of nine grahas with their own characteristics like an inborn innate behaviour. But each and every graha has the ability to mimic others (at times) based on their placements in the sky. For ex. Sun can sometimes act like Moon or Jupiter or even Rahu based on its placement, association, aspects etc. So let's talk about their characteristics first.
For readers convenience I'll use both the terms (graha and planet) here.
1. Surya (Sun)
Rahu and Ketu are shadow grahas, they exhibit their physical form on Solar and Lunar eclipses.