#1 Shawn Michaels
Shawn Michaels is so synonymous with stealing the show at WrestleMania that at least two of his nicknames, "The Showstopper" and "Mr. WrestleMania," are direct references to his ability to perform at the highest level on wrestling's grandest stage.
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It's worth noting, then, that his first Wrestlemania contest, at WrestleMania V in 1989 as part of The Rockers tag team with Marty Jannetty, stole precisely nothing, except maybe eight minutes of viewers' lives.
Taking on the team of the Twin Towers, made up of The Big Bossman and Akeem the African Dream (also known at one point as The One Man Gang), the big-versus-little dynamic never really clicked; Marty and Shawn tried a lot of the high-flying tandem offense which made them massively over in the AWA, but Bossman and Akeem weren't ready to play on that level and couldn't keep up with the smaller men's cardio.
The Twin Towers squashed the Rockers (literally, as a powerbomb and a splash put Shawn down for three, despite the match actually being fairly competitive) in a pretty standard Superstars of Wrestling match, although the Atlantic City crowd was surprisingly into this one (surprising considering how apathetic the same venue sounded a year prior).

He'd Get It Right When:
Shawn Michaels averages just under four Meltzer stars for his remaining 16 WrestleMania matches; the very next year, Marty and Shawn would put on an underrated opener with The Orient Express, and five years later Michaels would set the standard for WrestleMania success against Razor Ramon in the WWF's first pay-per-view ladder match.