- I'm Donna Troy, bitch.
Appearing in "Splitting the Atom"
- Harley Quinn
- Holly Robinson
- Karate Kid
- Mary Marvel
- Challengers from Beyond
- Batman (Earth-51) (Flashback and main story)
- Buddy Blank
- Buddy Blank's grandson
- Queen Hippolyta
- Monarch's Army
- Monitor Solomon
- Amazons of Themyscira
- Atomic Knights
- Joker (Earth-51) (Flashback only) (Deceased)
- Ace, Royal Flush Gang (Earth-51)
- Justice League of America (Earth-51)
- Justice Society of America (unidentified universe)
- Black Canary
- Doctor Fate
- Green Lantern
- New Earth
- The Bleed
- Multiversal Nexus
- Batarang (Earth-51)
- Batcomputer (Earth-51)
- Batrope (Earth-51)
- Batsuit (Earth-51)
- Brother Eye
- Crystal Ball of Merlin (Earth-51)
- Green Lantern Ring
- Helmet of Fate (Earth-51)
- Lex Luthor's Warsuit (Earth-51)
- Morticoccus Virus (First appearance)
- Nth Metal Wings (Earth-51)
Synopsis for "Splitting the Atom"
Ray Palmer and Kyle Rayner defeats and escape from members of the Crime Society. While located in a safe area, Ray then explains to Kyle on the reason he is involved in the Great Disaster is that he possesses knowledge of a cure to the deadly Morticoccus Virus after learning from the research notes from his Earth-51 counterpart.
Jason Todd explains and resolves with the Earth-51 Batman of his identity and the situations that is happening. In a argument of participating in the battle against Monarch, Jason tries to convince Batman into helping him in the fight.
In Blüdhaven, Brother Eye assimilates the remains of the city along with Firestorm and the Atomic Knights by incorporating their technologies into its power source. Karate Kid wonders why Desaad came to Blüdhaven, and is alarmed when he contemplates the possibility that Desaad deliberately left a Boom Tube generator for Brother Eye to assimilate.
Appearing in "The Origin of Doomsday"
- Bertron (Dies)
- Darkseid (Cameo)
Synopsis for "The Origin of Doomsday"
Bertron was an alien scientist who operated on the planet Krypton many thousands of years ago. He sought to create the ultimate life form. His first experiments however failed, but Betron cultivated cells from the dead experiment and infused them into his next test subject. This subject also died, but Betron, undeterred, repeated the process over and over again. Ultimately, his experiments were met with success. The life form, possessing the genetic memory of it's predecessors, had adapted beyond the previous experiments and was now immune to being killed by any process that had been used before. Biogenetically designed to be the ultimate survivor, this "Doomsday" slaughtered Bertron and escaped from the arid wastelands of Krypton.
He traveled across the stars for millennia encountering other races and creatures such as the Catalonians and their royal champion, the Radiant. Radiant defeated Doomsday at the cost of his own life, and the Catalonians performed an ancient funerary rite upon him, binding him in treated fabric and propelling him into outer space.
Doomsday survived this as well and ultimately came to the planet Earth where he instinctively sought out Earth's Kryptonian champion, Superman. The two fought one another to the death, but both Doomsday and Superman would soon return to life. 
- Issue shipped on January 16th, 2008.
- The tagline to this issue is "Mission Accomplished?"
- Keith Giffen is credited as story consultant in this issue.
- "The Origin of Doomsday" includes flashbacks to events from Doomsday Annual #1 and Superman (Volume 2) #75.
- Superboy-Prime begins referring to himself as Superman-Prime in this issue.
- The cover to this issue is inspired by the Marine Corps Memorial honoring the men who fought during the Battle of Iwo Jima in World War II. This iconic image has also been used for the cover to Invasion! #2.
- Items displayed in the Earth-51 Bat-Bunker include: Joker playing card, Brainiac's Head Ship, Lex Luthor's Warsuit, Mister Freeze's armor, Deathstroke's mask, one of Captain Boomerang's boomerangs and Black Manta's helmet.
- One of the Earth-51 flashbacks includes a pastiche of the first team-up of the JLA and the JSA as presented in Justice League of America #21-22.
- Discuss Countdown to Final Crisis Vol 1 15 on the forums
- Cover gallery for the Countdown series
- Images from Countdown to Final Crisis Vol 1 15
- Countdown to Final Crisis Recommended Reading
Links and References
The events from this issue or series are related to the Countdown to Final Crisis. Countdown was a weekly series spanning exactly 52 issues, and tying in with plots across many story arcs all over the DCU. This template will automatically categorize articles that include it into the Countdown Crossover category.