mixologist

A person who creates cocktails, especially one considered an artist in that craft.

Any bartender.

By the way, the difference between a bartender and a mixologist can be confusing, but normally a bartender serves the patrons at a sit-down style bar, where a mixologist would usually work at a very busy service-style bar.

But now we see a split in the mixed-drink community. On one hand, cool bars and star mixologists are lauded and awarded as never before. On the other, booze brands are rushing to develop pre-mixed beverages for a burgeoning Ready to Drink (RTD) market.

A disc jockey.