In 1992, he won the WDC, breaking virtually all records that could be broken in F1, in a single season.
After Frank Williams was being tight with salary negotiations (as per normal), Mansell left for IndyCar.
In his debut, 1993 season, he exceeded all expectations and won the PPG Indycar Series World Title.
For me, Mansell was the best all-round driver in 1992/3 (along with Senna, who probably had his best year in 1993 (skill-wise, not points-wise)).
It was the BTCC ref that fooled me - I seem to recall him being terrible at it