Oa forgive me, but what does it mean?!

It's a phrase that's echoed in comic stores and convention halls for decades, and soon it will find its way into movie houses world wide: The Green Lantern oath.

In brightest day, in blackest night,

No evil shall escape my sight

Let those who worship evil's might,

Beware my power... Green Lantern's light!

On June 17, movie-goers around the world will hear the phrase that kickstarts DC Comics' Green Lantern superhero life. The four-verse oath is such an important aspect of the Green Lantern mythos that something as simple as Ryan Reynolds reciting it from memory for a young fan at least year's Comic-Con International in San Diego generated legitimate buzz in comic book circles. But while Warner Bros. is hoping the oath said by Reynolds as Hal Jordan and others in the upcoming "Green Lantern" film becomes as well known as Superman's "Truth, Justice and the American Way," the mantra is more than just a catchphrase or byline for movie reviewers to feed to the general public.

Beginning with its first appearance way back in 1940, the Green Lantern oath has gone from being one hero's anthem to that of a multitude of men and women -- both on Earth and beyond. But the idea of an oath is separate and unique to the Green Lantern Corps; the closest thing to it is "Shazam!" by Captain Marvel or something out of a "He-Man" cartoon.

The Green Lantern oath as we know it today is far different from its original incarnation. In the first appearance of Green Lantern in June 1940's "All-American Comics" #16, Alan Scott -- the original Green Lantern -- had a much simpler oath:

...and I shall shed my light over dark evil.

For the dark things cannot stand the light,

The light of the Green Lantern!

At the time, the Green Lantern was a caped hero rather than the cosmic cop we know today. Scott simply recited the oath while charging his ring with a magic battery he had found while working on the railroads. It wasn't until after years of adventures that the oath changed into the memorable mantra we know today, first uttered by original Green Lantern Alan Scott and later by the next man to take the Green Lantern mantle -- Hal Jordan -- in 1959. It's widely presumed that sci-fi author Alfred Bester crafted the current oath with his stories featuring the Green Lantern in the early 1940s, but the writer himself refuted that assumption years later in an interview with journalist F. Gwynplaine MacIntyre.

DC later retconned the origin of the modern oath, tying its verses directly to Jordan, who explained that he crafted the oath based on some early escapades, with each line in the oath referring obliquely to ways he used the ring on particular cases. "In Brightest Day" referred to his use of the ring as a radar after being blinded by a magnesium bomb; "In Blackest Night" owing to his ring's ability to illuminate criminals while tracking them in a dark cave; and "no evil shall escape my sight" coming from his ring detecting shockwaves emitted by explosives used by a group of safecrackers he was chasing.

Around the same time Hal Jordan was launched as the new Green Lantern, DC also introduced the idea of a Green Lantern Corps -- a task force of ring-wielding space cops protecting the universe -- and the idea of an oath carried over to the Corps as a whole, though not the version fans had become used to reading. Owing to the alien diversity inherent in the Green Lantern Corps, comic writers established that many of the Lanterns had their own versions of the oath. Some, such as the one used by sentient plant officer Medphyll, were variations on the standard, while others veered into the undecipherable -- even by the Green Lantern ring's translation function's standards. It wasn't until "Green Lantern: Rebirth" in 2004, where the long-defunct Corps was re-formed, that the organization opted for the standardized version Jordan had been saying since 1959.

Over the decades, the oath has popped up in numerous places in pop culture. Perhaps one of the most memorable is Daffy Duck's memorable portrayal of Duck Dodgers reciting a variation of the oath after accidentally picking up Hal Jordan's laundry, causing the bewildered water fowl to temporarily become a Lantern in his titular animated series. After forgetting the real quote, the Duck invents his own, saying:

In blackest day or brightest night

Watermelon, cantaloupe, yadda yadda

Erm...superstitious and cowardly lot

With liberty, and justice, for all!

But the question remains: ultimately, what is the purpose of the oath? The corps members themselves have gone on record saying that the words don't function as some sort of He-Man-like power-up. Rather, it is a phrase that serves as a prayer or mantra with the intention of helping Corps members focus on the task at hand. Unlike the catalytic effect that saying "SHAZAM!" has for Captain Marvel, the Green Lantern oath is, in effect, a prayer or battle hymn, recited as a Green Lantern heads into battle, not dissimilar to the way a Catholic might gesture the Sign of the Cross before a trying or poignant moment.

Writer Ron Marz, who spent a number of years on the Green Lantern title and was the principal writer during the Kyle Rayner era, has a lot of experience with the oath -- and without it.

"When I took over 'Green Lantern,' it was with a mandate to go in a different direction than had been done before, so we left the oath behind because Kyle, frankly, didn't even know it," Marz told CBR. "Now that the Corps has returned, and Kyle is a part of it, I think the oath serves an important touchstone, something that serves to bind all the members. Whether you're a human from Earth, or a sentient vegetable from some far-off planet, everybody says the same oath -- and that's pretty cool!"

Longtime comics and movie writer Marc Guggenheim, who co-wrote the upcoming Green Lantern film, had a more succinct way of explaining his view of the oath, namely, in one of his own.

It's hard to say where the Oath comes from

Whether it's cool, or just plain dumb

I can't think of another hero who's got one

So I guess it's just part of what makes GL fun!

Experience the Green Lantern Oath for yourself when the movie opens in theaters on June 17, or share your take on the classic verses with fans online at The Green Lantern Infinite Oath site.