For an exceedingly brief time in very late 1972 and early 1973 Jim Steranko returned to Marvel Comics and became one of their go-to cover artists. He produced on average three covers a month for four or so months, for a relatively wide range of comics and genres. There are superhero covers, jungle covers, western covers, sword and sorcery covers, and horror covers. All in all a total of thirteen covers produced over five months, but a mighty four months indeed.
These covers are most memorable and linger in the mind long after the comics have ceased publication. Which is another common feature, aside from the Fantastic Four, not one of the features for which Steranko produced covers lasted longer than a few issues.
Why Steranko did these covers is a mystery to me, but perhaps he chose books that interested him or perhaps he merely took the assignment given him. Whatever the case these covers have proven to be durable pop culture items.
UPDATE: Thanks to new information, I realize I overlooked two of Steranko's SHIELD reprint covers. I've added them in. I'm very pleased indeed that I did this post, because I learned that Steranko produced the artwork for Fantastic Four #132, not something I realized before. That cover has been heavily altered by Marie Severin, but Steranko is in there.