Paul Ryan is the 54th Speaker of the House, but the top ten longest serving have dominated in the 226 years of history of Congress.
The ten longest serving have been in the Speakership for 81 of the 226 years, more than one third of the time!
They are, in order,with time rounded off:
Sam Rayburn 17 years
Thomas “Tip” O’Neill  10 years
John W. McCormack 9 years
Dennis Hastert 8 years
Champ Clark 7 years
Henry Clay 7 years
Carl Albert  6 years
Joseph Cannon 6 years
Thomas Foley  6 years
James G. Blaine 5 years
Six of these ten (Rayburn, O’Neill, McCormack, Clark, Albert, and Foley) were Democrats for a total of 55 years.
Three of these ten (Hastert, Cannon, and Blaine) were Republicans for a total of 19 years.
One of these ten (Henry Clay) was a Democratic Republican for a total of 7 years, later becoming a Whig as a United States Senator.
Clay, Blaine and Cannon were in the years from 1811-1911; Clark and Rayburn were in the years from 1911-1961, and McCormack, Albert, O’Neill, Foley and Hastert in the years from 1962-2007!
So modern Speakers on the average have served much longer periods than earlier Speakers!