<P> Glenn Franklin Howerton III ( born April 13 , 1976 ) is an American actor , producer , and screenwriter . He is known for his roles as Dennis Reynolds in It 's Always Sunny in Philadelphia , for which he is also a writer and executive producer , and Jack Griffin in A.P. Bio , as well as the lead role in the short - lived sitcom That ' 80s Show . </P>
<P> Glenn Franklin Howerton III ( born April 13 , 1976 ) is an American actor , producer , and screenwriter . He is known for his roles as Dennis Reynolds in It 's Always Sunny in Philadelphia , for which he is also a writer and executive producer , and Jack Griffin in A.P. Bio , as well as the lead role in the short - lived sitcom That ' 80s Show . </P>
who plays dennis on it 's always sunny
who plays dennis on it 's always sunny
Glenn Franklin Howerton III
Glenn Franklin Howerton III