I interviewed at DAP Acquisitions (Chicago, IL) in December 2017. Interview I applied online through LinkedIn and got called back three days later for a first round interview.
Dean Martin played Matt Helm as Dean Martin. He wasn't the cold and ruthless Matt Helm of the books. Instead he was a cool and randy fella who loved to drink, seduce some chicks, croon some tunes & fight some bad guys. I wouldn't have him any other way.
'Fraiser Crane' from Fraiser and 'Marshal Matt Dillon' from Gunsmoke played by Kelsey Grammer & James Arness respectively. They both played their characters for 20 years. There may be more examples, but clearly the answer to the longest is (most likely) 'Nancy Hughes' from As the World Turns.