As one of DC's resident time-travelers, it makes sense that Booster Gold has left an outsized impact on the DC Universe timeline over the years. While he's done some of this to protect the timeline from the influence of others, he's also sometimes done this to try and suit his own goals.
But in typical Booster Gold fashion, the hero's plans always seem to go wrong. Now, here are some of the dark realities that Booster Gold has prevented and inadvertently caused during his time-traveling adventures.
THE DEATH OF THE GREEN LANTERNS
In 2007's Booster Gold ongoing series, Booster was offered the chance to formally join the main Justice League. But upon discovering that his presence would lead to the death of Hal Jordan, Booster turned the heroes down and became a time-traveling protector. Working with Time Master Rip Hunter, Booster made his way across the timeline, preventing attempts made by the villainous Supernova to change the future and doom the various members of the Justice League.
One of the first that he encountered was a world where Guy Gardner had become Green Lantern first instead of Hal Jordan. In this world, Guy was introduced to Sinestro before he ever became a hero and ended up succumbing to an alien illness that hadn't affected Jordan. Sinestro turns on the rest of the Green Lanterns far earlier than he did in the original timeline and is able to build the Sinestro Corps before the Lanterns are powerful enough to repel them. The Green Lanterns are defeated and the Sinestro Corps conquers the entire galaxy, including Earth. However, Booster tricks Sinestro into thinking he's actually a fan of Sinestro's from the future and convinces him to not contact Guy Gardner, keeping the timeline on track.
SUPERBOY VS. LUTHOR
However, this, in turn, leads to another attempt to change the timeline of the DC Universe. Instead of targeting the direct history of Superman, Supernova instead caused the death of Jonathan Kent's ancestor in the old west, which ends the Kent family and prevents Superman from being raised by his traditional family. Instead, Lionel Luthor ended up stumbling upon young Kal-El crashed into the Earth in his rocket. Lionel adopts the child and names him Lionel Jr.
Luthor raises him alongside Lex, with the two boys growing up to be close. But when Luthor discovers that his brother is actually Superboy, he dedicates himself to killing the Kryptonian. Sadly, this version of Luthor would have been successful where almost all others were not by killing Superboy less than a year after he discovered the truth. Booster ends up heading into the old west to protect Jeb Westfield, the distant relative to the Kent family. Booster succeeds, and the battle even seems to be the thing that convinced Westfield to move back to Smallville and lay down roots in the small Kansas town.
BLUE BEETLE'S SURVIVAL
Booster eventually wanted to make his own changes to the timeline, like saving his best friend Ted Kord from being killed by Maxwell Lord. Working with Blue Beetles from across space and time, Booster succeeds and rescues Ted from their former friend and jumping back to what should have been their present. Instead, they discovered themselves in a timeline where Max's plans for OMAC were able to build longer. Instead of being exposed by Blue Beetle's death, Maxwell was able to take his time and fully unleash the OMACs.
Several heroes like Black Lightning, Black Canary, Green Lantern, Cyborg, Nightwing and Hawkgirl were confirmed as killed, and others like Wonder Woman, Robin, and Flash are shown being defeated by the OMACs. Even Batman, the creator of Brother Eye, is taken by surprise when Alfred is revealed to have been transformed into an OMAC. Maxwell Lord's telepathy even allows him to control Superman, making the Man of Steel his puppet.
Booster and Blue Beetle end up with the Resistance - Green Arrow, Hawkman, Pantha, Wild Dog, and Anthro - and try to storm Lord's base. But Green Arrow is converted into an OMAC, and most of the group is murdered. The few remaining heroes are recruited to stop Lord, with Doctor Light providing the killing blow. But so many of the heroes and allies are dead, and the Time-Stealers arrive to put down the survivors. In the end, Ted is forced to take his place back in the timestream and die by Maxwell Lord's hands, which sets him up to be discovered and defeated.
BATMAN'S GIFT
Even in the post-Flashpoint DC Universe, Booster can't help himself from trying to mess with the past. As an intended present to Batman before his wedding to Catwoman, Booster goes back in time and saves Bruce's parents from being murdered in Tom King and Tony Daniel's Batman #45. Booster intended to give Bruce closure over that possibility. But this new Bruce, never having become the noble figure he was in the core timeline, destroyed Skeets to prevent Booster from changing the timeline back. This leads to a world where Bruce leads a much happier life with his parents, but also a place where his potential allies are twisted and his enemies victorious.
The Joker has turned Gotham into a killing field, with his toxins infecting and corrupting numerous heroes. Dick Grayson has become a murderous Batman, who brings down criminals and infected superheroes with a casual lethality. Catwoman is a feral and ruthless serial killer. Jason Todd runs a successful anti-Joker bodyshop, Tim Drake is an uninterested cubicle worker and Duke Thomas has been lobotomized in an attempt to "cure" Jokerized people.
Penguin has become President, and Ra's Al Ghul rules over Eurasia with Talia by his side. A desperate Booster tries to introduce Catwoman to Bruce in an attempt to force their love, but Selina ends up killing Alfred and Thomas. Selina is in turn killed by Grayson, who fires wildly and also kills Martha, enraging Bruce and leading him to kill Dick.
Bruce has his experts rebuild Skeets, and demands that Booster -- who Bruce has held prisoner for a year in the caves beneath his home -- take him back a year so he can save his parents and kill Batman and Catwoman. But Booster and Skeets instead take Bruce back to the moment his parents were originally killed. Skeets is destroyed by Bruce - just as a version of Booster and Skeets arrive to change the past in the first place. The past Booster is shot and killed, and Bruce has to watch as his parents are gunned down.
While the timeline is reset and one pair of Booster Gold and Skeets remain to the present, the alternate Bruce Wayne gives into to grief and kills himself. The experience leaves serious psychological damage on Booster, who is then sent to Heroes in Crisis' Sanctuary to recuperate.