Answer by taking a quote from the following article:

James Thomas Fallon was born in the Bay Ridge neighborhood of Brooklyn, New York on September 19, 1974, the son of Gloria (nee Feeley) and James W. Fallon. He is of German, Irish, and Norwegian descent. His paternal grandmother, Luise Schalla, was a German immigrant from Osterholz-Scharmbeck, while one of his maternal great-grandfathers, Hans Hovelsen, was a Norwegian immigrant from Fredrikstad. Another set of great-great-grandparents were Thomas Fallon, an Irishman from County Galway, and Louisa Stickever, the daughter of an Irishman born in France and his Irish wife.

Late Night with Jimmy Fallon premiered in March 2009 to mixed reviews. Producer Michael Shoemaker felt that the show's style solidified when it used Susan Boyle as a joke. While other late-night programs had centered on her appearance, Fallon's Late Night debuted a sketch in which Boyle's emotional performances could "salve any affliction." It was this style of humor, that Adam Sternbergh of New York dubbed "the comedy of unabashed celebration", that led to the program's success.  Fallon proved himself different from other late-night hosts, with more of a reliance on music, dancing, impersonations, and games.  Between Fallon's own musical sensibilities and the recruitment of his house band, hip-hop collective The Roots, his incarnation of Late Night "evolved into the most deeply musical of TV's musical-comedy variety programs", with sketches in which he parodies Neil Young and Bruce Springsteen going viral online. Coincidentally, it was during the Tonight Show debacle that Fallon's show found its footing.  Another component built into the program was its association with social media and the Internet. The first majorly successful online clip was of Fallon and Justin Timberlake performing a "History of Rap". Online interaction and its presence on the show soon became crucial to its success. As of August 2013, Fallon was earning a salary of $11 million a year for his work on Late Night.  Fallon also hosted the 62nd Primetime Emmy Awards in 2010. In 2012, Fallon released his second comedy album, Blow Your Pants Off, which compiles many of his musical performances on Late Night. The album won a Grammy in 2013 for Best Comedy Album. Discussions for Fallon to take over The Tonight Show began in early 2013.

Did he hostmany important actors?
with sketches in which he parodies Neil Young and Bruce Springsteen going viral online.