#1 The Undertaker

The Undertaker became synonymous with the Show of Shows throughout his WWE career. His unbeaten streak is legendary and it often became a runner-up prize of sorts for those who didn't earn a major title shot at the event. Others even considered it akin to competing for a major title.
While he did not compete at last year's show, he did show up the following night on RAW in order to join the ranks who have interrupted Elias. He did also compete against Goldberg at the 2019 Super ShowDown event. Despite begin over 50, his name will always carry weight and anticipation regarding an appearance.
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Recently, reports have emerged that not only will The Deadman be at the Show of Shows this year but he will also get back into the ring. Some rumors have suggested that it would be against AJ Styles. That's a great idea for many reasons, including Styles being a safe ring worker as well as a huge name to have never crossed paths with the Undertaker.
He might be over 40 as well, but Styles is one of the most gifted in-ring performers of all time. Taker will be in good hands and will make the most of an appearance if he does indeed compete this year.