Boss of Black Organization
It would be so cool if it was either Mouri or Chief of Police,
Since the creator said the Boss has already appeared I think like everyone else its one of the main or recurring characters.
The Black Organization's formal name gives away the boss' name. "The Black Organization" is not the real name of the organization.
Minami Takayama, Gosho Aoyama's former wife and Conan's voice actor, knows the boss' identity.
Aoyama revealed that he didn't expect the Detective Conan series to last longer than three months.
This indicates that the boss might have been hinted early in Detective Conan.
The boss chooses the alcoholic codenames for the agents, but does not have one himself/herself.
The boss is not Professor Agasa.