You've likely seen his face here on Trends or in your social media feeds and his lip-synching skills are among the most widely known on YouTube. Last September, then-15-year-old Keenan Cahill posted a dubbed version of Katy Perry's "Teenage Dream" that became the Most Shared video of 2010.

Since that clip first became popular, his videos have been viewed one-quarter of a billion times. This month, he's averaged over 3 million views per week. Perry, whose tweet got the ball rolling, even made a video wishing him a happy birthday.

While he started with some simple lip-dubs, Cahill soon caught the attention of major celebrities who started appearing in his videos. It started with 50 Cent. Last week, Britney Spears briefly appeared in one. In January, Cahill's videos were viewed nearly 5 million times in just one day after his collab with DJ/producer David Guetta was posted.

Below we've pulled together the 10 most-viewed Keenan Cahill "duets" since last November:

(*Combined views. May take a moment to load in full.)