In the Comics Rupert Thorne was a politician not a Mob Boss.

Yet Rupert Throne continually becomes a Crime Boss in adaptations.

Batman The Animated Series seems to be largely responsible for popularizing it, yet they didn't do it first, first was Sam Hamm's original Script for the movie that became Tim Burton's Batman, where the Carl Grissom role was played by Rupert Thorne, (and Eckhart was Harvey Bullock).  But since then we've seen it in the Cold Open of the pilot of The Batman animated series, and in The Joker Blogs season 2, and other fan films.

But he was originally in the 70s and early 80s Comics a powerful corrupt politician, a member of Gotham's City Council.  Mayor Hamilton Hill was a corrupt mayor in his pocket, and Peter Pauling was a corrupt cop they arranged to have replace Jim Gordon as Commissioner.

I have no idea what caused this character to be so consistently changed in adaptations, it's not like the Comics don't provide enough Mob Bosses to work with.  In his most notable BTAS appearance he replaces Maroni in Two-Face's origin story.  And for a Mob Boss used only to be one The Batman takes down in the prologue right before the rise of The Joker, Falcone would have made more sense.  And for the Batman89 script, a Mob Boss employing the guy who shot the Waynes was Lew Moxon in the Pre-Crisis Earth-One continuity.  And The Joker Blogs was using him in it's version of the Mask of The Phantasm story, which itself was re-imagining elements of Year Two.

Seeing the political corruption in Gotham City would be a refreshing new subject for a Batman movie or Cartoon.  And you could easily connect him to a Mob Boss if you wanna keep that element going.

If I were in charge of the Court of Owls story-line, I might have connected Thorne to them.