Complex sentence: Jon Jafari is an American Youtube personality best known for the web series'JonTron', and as co-host of Game Grumps from July 2012 to June 2013.
Split into simpler sentences: Jon Jafari is an American Youtube personality best known for the web series JonTron. And as co-host of Game Grumps from July 2012 to June 2013.