The candy bar sold well, and the Heath bar grew in popularity. During World War II, it was even part of soldiers' rations (it was discovered that the bar had a very long shelf life).
Over a half century later (1983, to be precise), another candy maker decided that they wanted a piece of this particular candy action. The other candy maker was Hershey, and the bar they introduced was Skor. I remember the original TV commercials for Skor, and they called the toffee in the Skor bar "Swedish toffee." The commercials also featured a brunette model who, after one bite of a Skor bar, began turning blonder and more Nordic-looking. Her speech also changed, going from Standard American Dialect English, to English with a Swedish accent, to (presumably) Swedish with English subtitles.
Why did Hershey do this? As Steve Almond put it in Candyfreak, you can't patent a candy bar. You can trademark a name for a candy bar, but you can't make an exclusive claim to to the ingredients in that candy bar. And let's face it, there are other candy bars that are quite similar. For instance, Butterfinger and 5th Avenue are virtually identical, as are Hershey's Krackel and Nestle's Crunch.
As time went on, the company that produced the Heath bar went through a couple of changes in ownership. In 1996, it was purchased by Hershey, which produces both the Heath and Skor bars to this day.
Now, you might wonder why Hershey would continue to market two identical candy bars. Why continue to produce the Skor bar, if they are now producing the older (and probably better-known) Heath bar?
Well, guess what? They aren't identical. You don't have to take my word for it; all you have to do is take one Heath bar and one Skor bar, and break each one in half.
The toffee in the Heath bar is a lighter color, a very light tan with a touch of yellow. Both toffees contain almonds, but bits of almond are more readily visible in the Heath toffee. The Heath toffee also has a lighter taste to it.
The Skor's toffee is a much darker tan, only a couple of shades lighter than the milk chocolate covering it. It has a deeper, richer flavor than the Heath toffee, and almond bits are rarely seen.
Differences aside, the two bars do share a few similarities. The toffee in both seem to have the same degree of hardness -- the same amount of crunch between the teeth. And the milk chocolate does appear to same for both bars.
There are probably other differences and similarities that exist between the two bars. Documenting all of them, though, would take more analysis than I really want to devote to the subject. I would much rather sit back and enjoy one or the other -- or maybe even both.