While the Undertaker may be the one who outlived (outdeathed?) all the other the "Wrestling is not a day job" characters, due to his own longevity as a person and perfomer, it was commonplace at the time for people to have these more comic-book or secondary-profession based gimmicks. Look at the Mountie, or Brutus "The Barber" Beefcake, or the Big Boss Man. Fast forward a bit later on to people like Val Venis and the Godfather. It's basically the higher-rated version of the same thing.
Note: The following quote was taken from TV Tropes, my favourite website not named Wrestlezone Forums. It's written collaboratively - I did not write this.
TV Tropes said:
"Wrestling Doesn't Pay
"Professional Wrestling, as a vocation, apparently doesn't pay very well. How else can one explain the various wrestlers who apparently work a second job in their downtime? Stranger still, they bring the attire and mannerisms of their second job to the wrestling ring.
"This trope has long been a part of the wrestling landscape (as it makes for easy gimmicks), but it was especially common in the WWF in the early-to-mid-'90s.
"These wrestlers are more likely than any others to be a Steven Ulysses Perhero. (Note from Ollie: For non-Tropers this means basically that a character's name conveniently matches their gimmick, for example a denstist whose name is Isaac Yankem. Another Taker-relevant example is that Paul Bearer is supposed to be, by profession, a pallbearer. More commonly known as an aptonym, the Troper term can be written as S. U. Perhero.)
"This is actually a case of Truth in Television, as any indy wrestler will tell you. Conversely, within the landscape of the WWE, wrestlers can end up being paid very very well.
"Several of these gimmicks were actually the wrestlers' second jobs before they got to the big 2. Shane Douglas really was the dean of an elementary school. "
Ok, so how does this relate to the Undertaker?
And more importantly, why did he stand out amongst all the others? His gimmick was arguably just more of the same.
Well, I know he's now vaguely (vaguely) implied to be some kind of Southerner-turned-reaper-shinigami-esque thing, but as Tropes goes on to describe, he started:
TV Tropes said:
"as a wrestling ... well, undertaker, but eventually evolved into a wrestling personification of death, going through phases as a zombie, a cult leader, and, rather idiosyncratically, a biker along the way."
So Undertaker has reinvented himself, partly by necessity, partly by way of current coolness, along the way. For example, BikerTaker and Maskless Kane might be seen as WWE's own "Ultimate Marvel" versions of their Attitude Era selves - theoretically less implausible, and more realistic-looking in attire terms. BikerTaker is noticeably more grounded in the mundane as opposed to the older versions of the Undertaker, which I think reflects more effectively than anything else changing
attitudes (pun fully intended) in the wrestling business.
But in addition to all that, right from the start, there was something different. It's not just the height - even in the match against Giant Gonzalez, where the Undertaker looks like a freaking luchador by comparison - Taker just had this ...
aura. He was never
just a "Wrestling is my hobby, but I wrestle in my work clothes!" guy. The element of mystery has always been there. It's helped that not only has he been around so long, he's always played the character dead straight. I am not talking about sexuality there; what I mean is, any humour surrounding Taker, most likely from his Biker days, was always quite grim humour. The Undertaker, as a character, is NOT to be mocked. By anyone. And that's a rule that even the IWC seems to respect.
So I think that's stopped him from being taken 'unseriously' if such a word exists.
To summarise: Taker is just that good at his character that people are able to suspend their disbelief. It becomes accepted, even by new viewers. Most important factors:
- Longevity of character, builds respect for the performer
- Adaptability of character to fit current trends
- Sheer ability to play - no
be, the character.