Tequila is a tall intimidating member of the Black Organization that is used to muscle people into making deals with his syndicate. He apparently comes from Osaka since he is heard to speak with a Kansai accent. He first appears in Volume 12 of the manga (episode 56 of the anime) where Conan literally bumps into him at a video game convention in a hotel. At first, Conan only dismisses him as being a game company employee when he sees him pick up a suitcase with a game company's logo on it.
But when Conan overhears Tequila on a payphone, he hears him speaking to Vodka and that he is a member of the Black Organization. He then attaches a tracer to the sole of Tequila's shoe. Tequila then walks into one of the hotel's bathrooms as Conan listens in, only to see the bathroom explode.
Conan later found out that Tequila was conducting a cash-for-information transaction with a member of the video game company, and had accidentally obtained a briefcase that had a bomb in it that was intended for the man Tequila was doing business with, planted by another company employee. Later in Volume 37 he appears in flashback as Conan hears that the man they are looking for in that case received a visit from Tequila.