Most people probably think that Superman, Lois Lane and Clark Kent put the "eternal" in the eternal love triangle. But two books out this week demonstrate just how much Lois and Superman/Clark have changed over the decades.

The "Adventures of Superman" TV show of the 1950s and the film series that was launched in 1978 with "Superman: The Movie" have probably combined to form a specific, rock-solid image of the Man of Steel in the minds of most Americans. And yet, those Supermen are just two among many, as "Superman: A Celebration of 75 Years" ($39.99) ably demonstrates.

And the beauty of this tome is that it doesn't pretend otherwise. "Celebration" not only reprints almost 400 pages of important Superman stories from the past 7½ decades, but it also breaks them down into the significant Super-eras for us.

Few remember it now, but when Superman debuted he was, in fact, a Roosevelt-style New Dealer — a protector of the poor and oppressed, and a scourge of the callous, corrupt and monied interests that oppressed them. In his first two issues, he took on crooked politicians, a wife-beater and a system that was about to execute an innocent man.

All of that is reprinted here, along with the first story where Lois Lane suspected Clark Kent of being Superman (1942) and the first, full origin story for the Man of Steel in comic books (1948).

The next chapter is titled "Strange Visitor," and represents Superman's Silver Age (roughly 1958-1970), where the mythos was expanded exponentially. Superman, like the servicemen who returned from World War II to create 1950s suburbia, found himself pater familias to a growing family (beginning with Super-Dog Krypto and Super-cousin Supergirl). He gained a widening circle of friends, foes and pets; a more fleshed-out history for Krypton; a retreat called the Fortress of Solitude; and many other elements we now think of as standard fare for Super-stories.

The next three chapters are less seminal, as the Silver Age established most of the toys in the Super-sandbox. The stories reflect the times, with Superman suffering some of the self-doubt Vietnam-era America felt (1972), temporarily dying in the hype-fueled "Doomsday" tale in the go-go '90s (1993) and relaunching as an idealistic millennial blogger (2011).

A companion title, "Lois Lane: A Celebration of 75 Years" ($39.99), demonstrates she may actually be the more important — or at least more interesting — character, from a sociological sense.

The first chapter, "Girl Reporter," reminds us that she was the only cast member to debut in the same 1938 issue as Superman, and gives us a tough-as-nails "newshen," one who actually slips Clark Kent knockout drops in order to steal his scoop.

Unlike other tough chicks of her generation, like Rosie the Riveter, Lois wasn't immediately sent back to the kitchen after World War II. But her character was softened substantially. And then came the Silver Age, and a 180-degree flip for the character.

As the chapter "Superman's Girl Friend" demonstrates, Lois in the late 1950s and '60s transformed into a catty, conniving, flighty and ultimately embarrassing character, constantly scheming to uncover Superman's secret identity and/or trick him into marriage. While these silly stories were popular at the time, they paint a strange picture of the woman supposedly worthy of Superman's love.

After a decade of better stories, followed by a 1986 revamp, the Lois Lane who coincided with TV's "Lois & Clark: The New Adventure of Superman" was once again a sharp newshawk, and one with the insight and self-esteem to pass up the glamorous Superman to date Clark Kent.