Prime Taker went 7-9 years undefeated at WrestleMania.
Then again, it depends on what you consider Prime Taker.
90-97 was a GOAT prime as he pretty much never lost and defeated a prime Hulk Hogan a year into his career.
98-99 could be factored in but outside the ring distractions such as running a cult and satanic rituals caused him to lose a step.
Then you have the 05-08 career resurgence where he developed an elite level ground game to go along with elite striking even if his gas tank lost a step or two, but all around the late 00s was probably his prime technique wise.
Either way, any version of the Deadman is a tough out.