How many undertakers have there been in the WWE?

The Undertaker [ Mark Calaway ] made his debut in the Dallas, Texas based World Class Championship Wrestling (WCCW) under the ring name "Texas Red" in 1984.

Therefore meaning he started his career in 1984, which so far spans his career to a total of 24 years as of December 6, 2008.

Calaway made his WWF debut as "Cain the Undertaker" at a taping of WWF Superstars on November 19, 1990.