35 years ago - Arkillo is born on an unnamed planet with stone-age technology.
23 years ago - 12-year-old Arkillo comes of age & takes leadership of his tribe in ritual combat, beginning a brutal conquest of his entire planet.
8 years ago - 27-year-old Arkillo's countless atrocities finally draw the attention of the Green Lantern Corp, who intervene and imprison him on Oa.
5 years ago - 30-year-old Arkillo is moved off-planet to Citadel prison in anticipation of Hal Jordan's attack by the Green Lantern Corp.
3 years ago - 32-year-old Arkillo & Karu-Sil are freed from Citadel prison by Amon Sur to become one of Thaal Sinestro's lieutenants, armed with a simplified version of Sinestro's yellow ring.
1 year ago - 34-year-old Arkillo & Thaal Sinestro's forces battle the reunited Green Lantern Corp. He engages Killowog in 1-in-1 combat, and is imprisoned on Oa after his defeat.
The mid 2000's saw a gigantic explosion of supporting characters in the Green Lantern mythos as the world grew by leaps and bounds. At the time it was interesting to read, but in hindsight a lot of the developments of the era clash with the overall flavor of the Green Lantern story, so we're leaving almost all of it by the wayside. There are a few characters we're bringing along in one capacity or another, however, and Arkillo is one of them.
Arkillo's Comic History
After Geoff Johns rebooted Green Lantern in the pages of the 2005 miniseries Green Lantern: Rebirth, his biggest innovation was the invention of the different Lantern Corps, and it started in one of the earlier storylines in his Green Lantern run, the Sinestro War. Long-time Green Lantern arch-nemesis Sinestro created a whole army of yellow fear-based ring-weilders who challenged the Lanterns in a massive space battle. As Johns expanded his run and creaded a half-dozen other Corps, the characters created for the Sinestro Corp became major players on a landscape that really came to define DC in the late aughts before they rebooted their continuity in 2011, where they continue to play a role on the New 52.
There are a LOT of Sinestro Corp members but with very few exceptions they are primarily background characters; just concept art that was created as creepy looking characters to fill up the massive battle pages designed by Ethan Van Sciver, an artist fameous for near-lunatic levels of detail. Those characters were given names and backstories obviously, and there were even books created that gave us flashes of story about some of the more interesting ones, but by-and-large they are generally pretty forgettable. There are exceptions, of course, and when the gigantic death machine Arkillo engaged in a brutal fight with Green Lantern powerhouse Kilowog, he pretty much guaranteed that he would be one of the main members of the Sinestro Corp that we'd remember.
Our Arkillio Story
I've gone on in a lot of places about why we're not actually using the Sinestro Corp or other non-green corps in our timeline (diminishing the importance of the original corp, an over-reliance on cannon-fodder characters, etc). While Sinestro simply wouldn't ever share his power like that (nor COULD he, since he doesnt have a central power battery), there is absolutely a place for him to have lieutenants. He would certainly grant a few trusted warriors a fraction of his power just so they can operate in space and whantnot, leaving them to battle using their own power.
Arkillo, of course, has more than enough power to spare. The idea of him battling Green Lanterns using his own raw muscle and ferocity is absolutely awesome. He doesnt need to be in the story for long; really, it's just the one storyarc where Sinestro rebuilds a new army inside Qwardian space with his lieutenants which leads to Kyle restarting the Oan Power Battery. we kept him alive because he's a character that could easily be used down the road in another story.