<p>I like to think they are alternate reality versions of the same character. You know, like evil Spock with the beard. Two different timelines, one basic character, with some crucial differences, foremost being the precise native timezone. Although, the "hero" characters have noted lineages (for example the Nadirs or the Joneses), so its entirely possible Big Tony is simply Mr. Big's unacknowledged ancestor within the same timeline.
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