Rex Racer was the partner to Speed Racer Sr. back in the old times. He appeared in The Iron Terror pt 1-3. He is a guy who talks nonsense to Speed Racer Sr. And Speed Racer doesn't believe him.
His personally is he goes off crazy and he is ruthless and careless. He often times goes off to the power plant to check for the explosion and makes a plan in his board in the rv, that was on The Iron Terror Pt 1& 2. He was kidnapped by Zile Zazic ( Half Chim Chim & Half Zile) he was also kidnapped with Speed Racer Sr, Trixie Racer, & Spiritle. He is Speed Racer Sr. Partner back in the old times. He also fake his death in the 1999 Speed Racer and was never found again. He was also showed in The Iron Terror and found out that he didn't framed speed on Zile did in The Iron Terror. Speed Racer Sr. Though that Rex did it but it was not Rex it was Zile Zazic along with his robot Annalise that was replaced in The Hourglass Pt 3 and the aftermath is that everyting change there was no Ziles tower and was completely gone forever