The Scorpion
If the series was allowed to continue for longer, then it would have been awesome if, with the right amount of money, they introduced one or two supervillains from the comic.
The Scorpion would have been a terrific opponent, especially in a live-action series, just like Frye's creature was in the Hulk series.
I don't know who would be able to play Mac Rangan, but I would have loved to see Patrick Duffy in the role, if he wasn't doing Dallas, as he was a very well-built, athletic actor and I reckon he would have pulled it off as a villain.
It's ironic, because Lou Ferrigno once said that he wasn't too happy with the Spiderman series and felt that someone like Duffy could have played the webslinger.