2CELLOS (wiki) is a Croatian cello duo, consisting of classically trained Luka Šulić and Stjepan Hauser. They rose to fame after their January 2011 cover of Michael Jackson's Smooth Criminal became a hit on YouTube, receiving over 3 million views in the first two weeks and over 18 million views as of March 2016. Their 2014 version of Thunderstruck has over 57 million views.
Before they became partners, the two cellists were sometimes considered rivals, competing against each other in music contests.
This mashup blends Beethoven’s Fifth Symphony with Whole Lotta Love from Led Zeppelin. By the time they're finished, it’s four cellos.