The Fantasy on popular opera themes was one of the most admired genres of piano music in the first half of the nineteenth century. They were written and performed by virtuoso pianist-composers, and the genre enjoyed much popularity among concert-goers.
Wild
At some point in your life, if you are interested in music at all, you will have heard a tune or two by George Gershwin (1898-1937). What an absolutely unique composer freely mixing and combining classical and popular music styles.