Here’s an answer from Tyson, one of our great brewers.
As with all good beer, it all starts with malted barley (sorry Japan). The huge array of different malt varieties and the flavors and aromas they produce is like coloring with the big box of crayons. Bready, nutty, caramel, coffee, chocolate are just a few of the flavors/aromas that can be had and colors can vary from black to deep red to very pale yellow.
Next come the hops and they lack nothing in the sheer variety of flavor and aroma. Hops can be citrusy, piney, herbal, pungent, and many more.
Yeast is also a main determinate of flavor and aside from alcohol and carbonation, which affect perceived flavor, yeast flavors can range from banana, apple, and other fruity aromas to cloves and wet hay. All these ingredients and the characters they impart can be manipulated by the final piece of the puzzle, the process. Temperatures, mash thickness, pH, and many other small factors can make a big difference in the final product.
S,o the next time your drinking a beer try to appreciate the complexity that all started with some ancient Sumerian who screwed up making the bread.