Angel O'Day is the daughter of famed adventurer Professor Theo O'Day, and one half of O'Day and Simeon Private Investigations. Angel's father later married the retired super-heroine called Princess Power, and their common child was the super-strong but mentally deficient girl Athena Tremor, later known as Dumb Bunny of the Inferior Five.
After leaving his first wife and their daughter, Athena, Professor O'Day remarried and his second wife gave birth to Angel. Angel's mother died during her infancy, leaving her remembering little to nothing about her. Professor O'Day was devastated, but continued taking Angel on trips. During a trip to Africa, Angel stumbled into the vicinity of Gorilla City and encountered a gorilla who could apparently speak. The O'Days and their guide, Msomi, treated a snake bite the gorilla received. They end up taking the gorilla, Sam Simeon, in as part of their family.
Professor O'Day reconnected with his first wife and they remarried, Angel and Athena being raised as sisters. With most of her family members having superhuman strength, Angel O'Day developed a massive inferiority complex, which she tried to compensate by over performing in school and in arts such as fencing, martial arts, sharpshooting and foreign languages. This also led to a strained relationship with her half-sister.
While working as a translator for a shipping company, she uncovered a massive smuggling operation. With the reward money, she opened up a detective agency, O'Day and Simeon Detective Agency, something she has never regretted. Her father's best friend, famed Chinese detective Charlie Chum, taught Angel all he knew about detective work.
O'Day and Simeon Private Investigations
Angel and Sam took on a number of cases, including investigating the attempted murder of a man,  the disappearance of multiple go-go dancers,  a circus family on a crime spree,  a number of kidnappings,  and the mysterious murders on Angel's cousins, the Avarice family. When conspirators were after Charlie Chum, he reached out to Angel to deliver his sensitive papers. Angel was able to expose the mastermind as Chum's youngest "son", who in reality was someone posing as his son, taking advantage of Chum's absentmindedness.
In her personal life, Angel has gone on dates with a few men, including Alec Sharp, a news photographer, Rocky Tier, who turned out to be a con artist named Bernie Bunko, and police detective Komicz.
During an alien attempt to pull Earth out of it's orbit, the fabric of time and space became unstable, and heroes and villains from the past, future, and other Earths collided. Angel and Sam use their detective's agency to shelter many of the displaced, such as Anthro, Firehair and Binky. Angel's half-sister Athena and the Inferior Five also gather in the agency. Angel leads Bat Lash and Tommy Tomorrow on a mission to save the world, leaving Sam, Athena, and the others to watch the displaced.
They discover a giant green monolith that's casting a field around the Earth as it's pulled through space. At the same time, the Challengers of the Unknown and Lois Lane arrive and both teams agree that someone must brave the interior to save the world. Tommy Tomorrow realizes that the green structure is made of a self-regenerating material; any hole they make in it can only stay open for a brief moment before closing. Angel and Lois Lane enter through their team's hole before any of their male counterparts have time to object.
The two fight their way through opposite ends of the structure, battling security robots and intense radiation. As they begin to succumb to the radiation, the two encounter each other in the central control room. Angel ultimately shuts it down, causing it to collapse. Lois Lane barricades them under a console and all the displaced heroes fade back to their own times and Earths.
During the Crisis on Infinite Earths, after New Earth had been formed, Angel was at the Detectives Convention in Las Vegas when Jonni Thunder found Angle Man's Angler weapon. Meanwhile, Sam was in Gorilla City with Detective Chimp trying to make sense of Solovar's injuries and the Earth being pulled into the Antimatter Universe.
Reuniting with Athena
Despite Angel's rocky relationship with Athena, Sam Simeon's relationship with was positive, and they would meet Tuesdays for lunch, much to Angel's dismay. Athena admitted to Angel that she would ask Sam to be her boyfriend, which Angel was highly opposed, but swore not to undermine the venture. Around the same time, agents from Gorilla City and Gorilla Grodd were racing to capture Sam because of the mental capabilities he inherited from his grandfather Grodd. Setting aside their differences, Angel and Athena teamed with the Inferior Five to rescue Sam.
As they prepare their plan, Angel and Athena begin to reconcile their rough past. However, Grodd probes Sam's mind and discovers that Sam had feelings not for Athena, but for Angel. This causes Athena to fly into a rage, but Merryman blocks her from Angel, refusing to move. Athena turned her rage on Grodd, but he responded by snapping her neck, seemingly killing her instantly. Angel, Merryman, and White Feather are imprisoned and mourn her. White Feather tells Angel that Merryman loved her, but swore Blimp, Awkwardman, and himself to secrecy.
Athena regains consciousness, revealing that Grodd merely paralyzed her. Angel hits the nerve in her knee to make her kick the wall down. Free, Angel uses fighting techniques she and Sam created for dealing with larger foes, giving Sam enough time to undo Grodd's plans and heal Athena. Grodd planned to use a mysterious 'Green Glob' to transform 3/4 of humanity into Gorillas, but having stopped the plan and set the glob free, Sam was rewarded by being transformed into a human, where he and Angel embraced and kissed before he was reverted back to a gorilla.
Over time, O'Day and Simeon Private Investigations was able to expand, hiring secretary Bernice "BJ" White, and booking higher paying jobs, such as locating the missing model Bambi Dexrous and solving her murder.
- Investigation: Angel is a superb detective with a keen eye.
- Multilingualism: Angel is very intelligent and well-educated, knows twelve languages (Mandarin and Cantonese Chinese, Japanese, Dutch Afrikaans, Swahili, Ancient and Modern Greek, Latin, Spanish, German, Russian, and Atlantean),
- Marksmanship: Angel is an excellent shot.
- Martial Arts: Angel is a superior hand to hand combatant, with extensive knowledge of karate and Kung Fu, plus a special martial art adapted to battle gorillas.
- Fencing: She is also an "A"-rated fencer.
- .45 Super: Stainless steel Detonic 45 ACP as her prime weapon.
- Although this character was originally introduced during DC's Earth-One era of publication, their existence following the events of the 1985–86 limited series Crisis on Infinite Earths remains intact. However, some elements of the character's Pre-Crisis history may have been altered or removed for Post-Crisis New Earth continuity, and should be considered apocryphal.
- Appearances of Angel O'Day (New Earth)
- Images featuring Angel O'Day (New Earth)
- Quotations by or about Angel O'Day (New Earth)
- Character Gallery: Angel O'Day (New Earth)
- Angel and the Ape (Volume 2) #1
- Angel and the Ape (Volume 2) #1
- Showcase #77
- Angel and the Ape #1
- Angel and the Ape #2
- Meet Angel #5
- Angel and the Ape #3
- Meet Angel #4
- Meet Angel #6
- Showcase #100
- Crisis on Infinite Earths #11
- Angel and the Ape (Volume 2) #3
- Angel and the Ape (Volume 2) #4
- Angel and the Ape (Volume 3) #1