Rule No. 1: People rarely change.
Chances are he's been missing deadline for 20 years and others have tried before and failed to get him to make deadline. Therefore you have a very tough challenge ahead of you.
So you need to make a decision: What's more important to you, making deadline, or getting out of your comfort zone and dealing with the problem?
It may be he'll never make deadline, which will set up another choice: Do you keep his same duties and accept late copy, do you move him to less time-sensitive duties or do you get rid of him?
Do you really want to go to your boss and say, "Old Joe's a nice guy and well-respected, so I'm not ever going to make a Friday night deadline?"
Also, there's a difference between being assertive and being asshole. Be assertive, but don't be an asshole.
In terms of practical steps, maybe you give him earlier deadlines or multiple to complete the various tasks he has. For instance, if his Friday deadline is 10:30 p.m. and he's to file two stories, make one come in by 9 p.m.
Try to create an environment where he can succeed, but impress upon him the fact that he needs to make deadline.