#4 Anything before WWE
WWE acquired WCW and uses its history for guys like Booker T, Sting or Goldberg. But they never mention the Undertaker being part of WCW before his WWE days. Mark Calaway wrestled for six years in different promotions before WWE. He was on the WCW roster for a year as a part of The Skyscrapers alongside Sid Vicious and others.
He wrestled under the ring name ‘Mean Mark Callous’. He was also managed by the likes of Teddy Long, Dutch Mantel (Zeb Colter) and even Paul Heyman, at various points in his career. Undertaker was briefly associated with the NJPW before joining the WWE.
WWE made Mark’s career; he owes his success to the Undertaker character and WWE. The Undertaker is a true WWE ‘guy’, and his character foreshadows everything he has done in the past.