He's actually a more serious character in the book. A lot was transferred to the series (the original, not that crap remake!) and you see Leonard Rossiter as you're reading it, but he's far more of a tragic character in the novel. It's sometimes interesting to compare the movie/TV versions against the books, but I don't normally watch something I've read because books are always so much better.
In this case I was given the book long after the TV show, and had it on my shelf for years before I decided to read it. Well worth it if you can get hold of it.
It's really about a man going through a mid-life crisis. There are things about him and his attitude that I can associate with, like Victor Meldrew, that's what probably made him so popular.
The sad thing is, the story hasn't dated at all!! In fact it's probably more relevant today than in the 1970s!