Rahu is not the actual planet but is an imaginary planet. Rahu is a node
that is positioned where the earth's trajectory around the Sun and the
Moon's trajectory around the Earth meet. According to Indian mythology,
Rahu represents the head of a demon. Rahu is responsible for Solar eclipse.
When Rahu, Sun and Moon are in the same zodiacal longitude Solar eclipse
Rahu is a 'shudra graha', hence people influenced by Rahu behave like
illiterate and uncultured people. It rules over thieves, witches, magicians,
venom and poison, snakes and thorny bushes, jails and isolated places,
unhabitated places, cemeteries, hypnotists etc.
According to the Puranas, Rahu is instrumental in strengthening one's power
and converting even an enemy into a friend. Rahu is often called the Planet
of Success. Rahu doesn't rule any zodiac, since it is not a real planet.