As pictured in this infographic, The History of Portable Music, we can see that what once was dominated by Sony, is now dominated by Apple.
Back in the day, “Walkman” was the default term for any portable music player, whereas now, many people generically refer to portable mp3 players as an “iPod.”
Sony was able to continue its dominance as technology transitioned from cassette to CD, but when the jump from physical media to virtual came, Apple took the Pole Position and never looked back: