Robert B. Parker's Spenser comes to mind, a character marked by his imposing presence, wry attitude, and Irish heritage. Spenser's first TV incarnation, as played by Robert Urich, looked the part but lacked the attitude. His second appearance, in three mediocre A&E movies starring Joe Mantegna, had more edge but was totally off physically.
Incidentally Hawk--Spenser's contemporary cohort played indelibly by Avery Brooks in the Urich series--was played in the first A&E movie by Shiek Mahmud-Bey, easily at least fifteen years Mantegna's junior.
...Hawk didn't have a large role in the movie. Many of the roles in the A&E movies seemed miscast. I guess these were the best actors to be had on a basic cable budget after paying Mantegna.
Then again, since Mantegna himself was miscast, it's difficult to imagine who could've played Hawk to his Spenser.
In the third A&E movie, Hawk was played by Ernie Hudson.
...Mantegna did make a go of it and I thought he was better than Urich at playing Spenser's wisecracking attitude. Robert B. Parker himself wrote the script, and while I was none too impressed, I don't think the script impacted Mantegna's performance. He just couldn't overcome not being a big Irish guy...
On the flipside, I think Tom Selleck has proven Parker's other series protag, Jesse Stone, is not tied to his appearance. The Jesse Stone of the books is 25 years Selleck's junior, and yet Selleck plays his mix of quiet strength and alcohol addiction about as well as you can ask. I think part of his success is having more control over production than Mantegna did and knowing how best to use it in service of the movie. The Jesse Stone scripts are not written by Parker but sure do sound like him.