In the science fiction television show Stargate SG-1 and original movie Stargate, Ra was a fictional alien related to Ra of Egyptian Mythology.
Ra was killed in the original film Stargate. The premise for the movie was that Ra was actually an alien who posed as a god to enslave the peoples of Earth. He was overthrown on Earth but, still ruled over Abydos to which, Daniel Jackson, Jack O'Neill, Kawalsky and others travelled.
They managed to communicate with the locals who were being forced to mine Naquadah for Ra. He was going to attach some of the mineral mined in the area to a nuclear bomb and send it back to destroy earth. It was instead sent up into Ra's Hatak by way of a ring transporter.
As a side note, beyond glowing eyes and the bass augmented voice, when Ra became angry the outline of the real alien Ra could be seen within the host. This portion appears to be in direct contradiction to the Stargate SG-1 series, as the true Goa'uld appears to be a serpent-like creature which occupies the brain stem in order to control the host.
According to Stargate SG-1 canon, Ra was the most cunning and ruthless of the System Lords, so much so that he was awarded the title Supreme System Lord and became something of a king-emperor among the Goa'uld.