After a disappointing first month of sales, the Walkman went on to become one of Sony's most successful brands of all time, transitioning formats over the years into CD, Mini-Disc, MP3 and finally, streaming music. Over 400 million Walkman portable music players have been sold, 200 million of them cassette players. Sony retired the classic cassette tape Walkman line in 2010, and was forced to pay a huge settlement to the original inventor of the portable cassette player, Andreas Pavel. But the name lives on today in the form of new MP3 players and Sony's Walkman app. They heyday of the Walkman may be over, with kids today baffled and disgusted by the relative clumsiness of cassettes. But the habit it spawned — listening to music wherever and whenever you want — is bigger than ever.