Of course we know Rick Astley for his song "Never Gonna Give You Up" but he's recently made a comeback from something called "Rickrolling" (see the definition below). He was in London for 'Let's Rock London' and did a pretty killer cover of Bruno Mars "Uptown Funk."

The true definition of "Rickrolling" according to Wikipedia:

Rickrolling is an Internet meme involving the music video for the 1987 Rick Astley song "Never Gonna Give You Up". The meme is a bait and switch; a person provides a hyperlink which is seemingly relevant to the topic at hand, but actually leads to Astley's video. Rickrolling has extended beyond web links to playing the video or song disruptively in other situations, including public places, such as a live appearance of Astley himself in the 2008 Macy's Thanksgiving Day Parade in New York. The meme helped to revive Astley's career.