According to the creator of the the DC hero Hourman.

In an interview with ComicBook.com, Sentry creator Paul Jenkins explained how the initial idea for his 2000 Sentry series for Marvel actually started at DC.

Jenkins spoke about how the development of the series took several years, before the project finally got off the ground. Notably, the debut Sentry storyline placed the character at the very heart of the Marvel Universe, and now, decades later, the MCU could potentially be ready to make good on that, if the character plays a prominent role in the Avengers films.

Following His Successful MCU Debut, Sentry's Creator Reveals The Character Nearly Belonged To DC Instead

A Major Comic Book History "What If?"

Sentry creator Paul Jenkins described in his interview with ComicBook.com. As Jenkins put it, he originally conceived of the story that would become The Sentry while working at DC Comics; this initial version would have used the DC character Hourman, a hero with decades of history up to that point. As Jenkins put it:

That first series I had created years before its release, I had pitched it as the Hourman for DC because I was writing Hellblazer at the time and I was looking for other things to write, other things to pitch them. I didn’t know a lot about comics and that is a benefit to my work, it allows me to get to these characters and interpret them from a new perspective. I’m not weighed under the continuity. I pitched Hourman and I thought, because he takes a pill to give himself superpowers, this is the perfect story about addiction.

For readers familiar with Sentry’s lore, this makes a lot of sense.

In The Sentry, the eponymous character is initially positioned as having been a key hero in the Marvel Universe, in the past, before all trace of him was wiped from the collective memories of Marvel's populace. This was a novel concept, one that immediately gave the series a sense of place in the publisher's vast ongoing continuity; however, it turns out the genesis of it stemmed from a pre-existing character, one who did in fact have the prior connection to the Justice League the way Sentry was said to have had with the Avengers.

The MCU Can Help Bring The Sentry's Origin Story Full Circle

The Cinematic Sentry Should Be A Major Player

DC Comics rejected Paul Jenkins' original Hourman pitch, but it was, in fact, DC's editors that suggested the author create his own character for the story. From that point, the story bounced between the two major publishers before finally landing at Marvel. According to Jenkins:

Ultimately, [using Hourman] didn’t fly at DC and my editor at the time suggested I just create a new character. So what you see in The Sentry #1 is the exact same for Marvel what it was for DC.

Twenty-five years later, the Sentry isn’t quite a fixture of the Marvel Universe, though the character’s appearances are generally well-received. The MCU, however, could change that; reaction to the cinematic Sentry beyond just the Marvel fandom has already been positive, suggesting he will feature prominently in near-future plans for both Marvel Comics and the MCU.

The Marvel Cinematic Universe version of the Sentry, and his dark counterpoint the Void, have the potential to fulfill the character's original role in Marvel lore, as envisioned by the backstory to first The Sentry miniseries.

In fact, the Marvel Cinematic Universe version of the Sentry, and his dark counterpoint the Void, have the potential to fulfill the character's original role in Marvel lore, as envisioned by the backstory to first The Sentry miniseries, by taking center stage in the next Phase of the MCU as its strongest hero, and perhaps its most dangerous villain. Whatever the Sentry's MCU storyline amounts to, it is made that much more fascinating by the knowledge that he was initially going to be a DC Comics character.

Source: ComicBook.com