Mr. Zero interviews the drivers for questions like his/her motivation for racing, or what he/she thinks of the other characters. Sometimes he will ask for an autograph that will be sorted to a lucky viewer. When in the presence of evil drivers, like Black Shadow or Deathborn, he trembles in fear.
In F-Zero (outside the comic) and F-Zero Maximum Velocity, Mr. Zero is replaced by a robotic announcer. It is unknown why he dosn't announce the races himself in F-Zero, as he is present.
Mr. Zero is a cyborg, with green hair and a turquoise suit. His enhancements are goggles and a microphone, prehaps aiding in announcing the races. Depending on the difficulty level the player finishes the Grand Prix, Mr. Zero will be wearing a different suit.
(Green for Novice, Purple for Standard, Light Purple for Expert, and White for Master.)
He also wears shoes that actually look like F-Zero machines, according to Lap 20 in the anime.