Supergirl/Power Girl is one of the most popular heroines in the world. But over half century of continuous publication, as well as the existence of several alternate universe counterparts and short-lived, wildly different replacements in addition to several retcons driven by constantly-changing editorial policies is going to make keep their different versions straight a difficult task.
DC created -and retconned out straight after- a few Supergirl characters during the Golden Age and early Silver Age until Otto Binder and Al Plastino created Kara Zor-El in 1959. Her origin was very barebones, though, and further details such like her full name, her mother's or her hometown's were added over the years.
For many years both characters kept consistent backstories and identities until it was decided in the 1980s that Superman needed to be the sole Kryptonian survivor again. In 1985, Crisis on Infinite Earths happens. The Multiverse is destroyed except for a single Earth. Supergirl dies in battle. Power Girl is spared, but editorial dictates she no longer can be Superman's alternate reality cousin.
Since that point on and for nearly two decades, DC will try to replace Kara Zor-El with one non-Kryptonian Supergirl after another. Her substitutes will be given increasingly convoluted backstories and identities, and neither of which will last for longer than a few years at best. Power Girl's origin will be retconned in 1987 to being Atlantean sorcerer Arion's granddaughter born 45,000 years ago, a backstory which will be also retconned several times over the years.
In the early 00's, DC relaxed their policy regarding other Kryptonian survivors, and Executive Editor Dan DiDio decided the then-current Supergirl wasn't marketable due to her convoluted backstory involving protoplasmic shape-shifters and flaming angels, and a simpler approach was needed.
In 2003, Power Girl's Atlantean origin is retconned out. One year later, Kara Zor-El is reintroduced in Superman/Batman Vol 1. Unfortunately, conflicting writers retconned her backstory several times until Sterling Gates established her definitive origin in 2009. Around that time, Power Girl's status as cousin of the original Superman was restored during Infinite Crisis.
In 2011, The Flashpoint event reboots the DC universe, creating Prime Earth and changing most of characters' backstories. Supergirl is still cousin of the Prime Earth Superman, and the only person to claim the title, and Power Girl is cousin of the Superman of Earth 2. A second Powergirl named Tanya Spears takes up the mantle.
- 1949: The first character to be named Supergirl is created. Lucy of Borgonia was a non-powered human girl who made no further appearances.
- 1958: Otto Binder and Dick Sprang create Super-Girl as a means to gauge public interest in a female Superman character. Super-Girl was wished in existence when Jimmy Olsen was given a wish-granting mystical totem staff and wished Superman might find a female partner. Super-Girl materialized out of nowhere, possessing the same strengths and weaknesses as Superman. Later she sacrificed herself to save Superman from a Kryptonite meteor, and Jimmy wished her out of existence before she died from Kryptonite poisoning. Later this story was deemed out of continuity.
- 1959: Kara Zor-El is created by Otto Binder and Al Plastino. Her origin has her born more than one decade after Krypton's demise to Superman's uncle Zor-El and an unnamed woman on an unnamed Kryptonian town that survived Krypton's destruction. When Kara -no surname given still- was fifteen, a meteor shower ripped the lead plating covering the city's radioactive soil. Her parents built a rocket and sent her to Earth, where they had just discovered another survivor had settled on. Subsequent stories added or changed details.
- 1962: The Unknown Supergirl. Kara's origin is retold, Argo City is finally named and a minor detail is changed: Zor-El and his wife had been watching Superman for some while prior to Argo's demise and knew he was their nephew. Her mother Alura In-Ze -later renamed Allura- is also given her name.
- 1964: The Untold Story of Argo City tells the definitive version of Pre-Crisis Supergirl's origin and reveals her parents are still alive. Kara gets her parents out of the Survival Zone and they move to Kandor.
- 1968: Kara Zor-El's full name is given for first time in a Legion of Super-Heroes feature.
- 1976: Power Girl is created. She was born and left Krypton at the same time as her cousin, but her ship took longer to arrive. Her "Symbioship" was designed to hold her in stasis during her development through the long voyage, running a virtual reality program which allowed her to interact with life-like copies of her parents and fellow Kryptonians. By the time she landed on Earth, Kara was in her early twenties. She agreed to be Superman's secret weapon for her training's duration until she revealed herself to the J.S.A.
- 1985-1986: Crisis on Infinite Earths. Kara Zor-El dies in battle. Earth-Two and all alternate Earths are destroyed. Kara would make cameo appearances every so often, but by and large her existence is erased from History and memory.
- 1987: Power Girl's origin is changed. Now she is Atlantean sorcerer Arion's granddaughter. Born 45,000 years ago, her grandfather put her in a symbioship and sent her to the future in order to save her from his half-brother Garn Daanuth, deceiving her into believing she was Superman's cousin.
- 1988: The Supergirl Saga and first Kara's replacement. Superman meets Matrix, a protoplasmic shape-shifting life-form hailing from an alternate pocket dimension and created by an alternate universe Lex Luthor
- 1990: Keith Giffen creates Laurel Gand/Andromeda as a replacement for Supergirl in the Legion of Super-Heroes. Laurel's backstory is nearly identical to Kara's except for being Daxamite's Mon-El's cousin.
- 1995: Legion of Super-Heroes' continuity is rebooted due to Zero Hour. A new Laurel Gand is introduced, also Daxamite but with a very different past.
- 1995: First Superman/Aliens crossover. Superman meets an alien girl called Kara, born in a floating city named after the original Kryptonian Argo City. Kara's hometown survived the destruction of the planet Odiline only to be besieged by a murderous alien species. At the end of the story, Kara goes missing. Superman wrongly believes her dead, and he never brings her up again.
- 1996: Matrix meets a dying girl named Linda Danvers and merges with her to save her life. Later, she learns Linda was a Satanist who got murdered by her boyfriend,, but Matrix's sacrifice has turned both of them into an Earth Angel.
- 1998: During the DC One Million event, a new Supergirl makes an appearance. Later it would be revealed her name is Ariella Kent, she is daughter of Linda Danvers and an alternate Pre-Crisis Superman, and she is wandering over the Multiverse.
- 2002: Many Happy Returns. Kara Zor-El reappears for a short while.
- 2003: Linda Danvers takes off for unknown parts and is replaced with Cir-El, a girl who believes to be Clark Kent and Lois Lane's future daughter.
- 2003: Arion reveals Power Girl isn't his granddaughter or Atlantean for that matter.
- 2004: It is revealed Cir-El is a girl born in a possible future and genetically modified with Superman's DNA. Cir-El sacrifices herself so a bad future never comes to pass, and erases herself from history.
- 2004: The Supergirl from Krypton. A new Kara Zor-El is introduced. This incarnation was born on Krypton over fifteen years before Superman and was sent by her parents to take care of her baby cousin, but a Kryptonite asteroid caused her rocket to get delayed. She was put in suspended animation but the Kryptonite radiation damaged her memory.
- 2005: Power Trip. Power Girl is plagued by Psycho Pirate, who reveals she is the Supergirl from Earth-Two.
- 2006: Infinite Crisis. Power Girl's Pre-Crisis past is fully restored.
- 2006: Girl Power. Dark Supergirl turns up and claims Supergirl's father hated his brother and wanted her to kill her cousin, but Supergirl refuses to believe her evil duplicate.
- 2007: Breaking the Chain Kara Zor-El is told by someone resembling Zor-El that he sent her to kill her cousin because his body hosts evil spirits from the Phantom Zone.Later it would be revealed that Zor-El was fake and his story a lie.
- 2008: Supergirl's earlier origin is retconned out in favor of another where her father charges her with acting as Krypton's representative on Earth and looking after her infant cousin, and her uncle Jor-El hopes they can live through her.
- 2008: Brainiac and definitive Post-Crisis Supergirl's origin. Superman and Supergirl defeat Brainiac and rescue Kandor. Superman meets the real Zor-El and Alura In-Ze, who tell her daughter lived in Argo City with them after Krypton's explosion, and she was sent to Earth when Brainiac raided the floating city.
- 2009: New Krypton. Zor-El's story is confirmed as Kara's true origin. It's established she spent thirty-five years in suspended animation and her conflicting memories were hallucinations induced by Kryptonite-poisoning.
- 2011: Flashpoint happens. Supergirl and Power Girl are given new backstories, but their ties to Superman remain unchanged. Supergirl was fifteen-years old when her father sent her to Earth right before Krypton's explosion. Her rocket spent many years circling around the Sun in order to collect enough sunlight to activate her powers, and then it crashed into Siberia. She is her Earth's first and only Supergirl. Power Girl was a little child when she left Krypton and still a child when she crashed on Smallville many years later thanks to suspended animation. Jonathan and Martha Kent volunteered to take care of her until her teenhood. Afterwards, she moved with her cousin and his wife, called herself Supergirl and operated as Superman's secret weapon for a while. She took the "Power Girl" moniker when she and her best friend Huntress were temporarily stranded in Prime Earth.
- 2014: Karen Star returns to Earth-Two and Tanya becomes the new Power Girl after receiving powers.
- 2018: Due to history being altered by Superman: Reborn, the Earth-2's Power Girl is erased from the new timeline.
- Supergirl Recommended Reading
- Action Comics (Volume 1)
- Adventure Comics (Volume 1)
- All-Star Comics (Volume 1)
- Supergirl (Volume 1)
- Superman Family (Volume 1)
- Supergirl (Volume 2)
- Infinity Inc. (Volume 1)
- Power Girl (Volume 1)
- Supergirl (Volume 3)
- Supergirl (Volume 4)
- Supergirl (Volume 5)
- Supergirl and the Legion of Super-Heroes (Volume 1)
- Power Girl (Volume 2)
- Supergirl (Volume 6)
- Worlds' Finest (Volume 1)
- Supergirl (Volume 7)
- Minor Detours: Who Is Your Daddy?
- Superboy #5
- Superman #123
- Action Comics #260
- Action Comics #252
- Action Comics #285
- Action Comics #291
- Action Comics #309
- Action Comics #310
- Adventure Comics #365
- All-Star Comics #58
- Secret Origins (Volume 2) #11
- Superman (Volume 2) #21
- Legion of Super-Heroes (Volume 4) #9
- Legion of Super-Heroes (Volume 4) #66
- Superman/Aliens #2
- Supergirl (Volume 4) #1
- Supergirl (Volume 4) #7
- Supergirl (Volume 4) #9
- Supergirl (Volume 4) #1000000
- Supergirl (Volume 4) #75
- Superman: The 10¢ Adventure #1
- JSA #50
- Superman (Volume 2) #200
- Superman/Batman #8
- Superman/Batman #9
- JSA Classified #1
- Infinite Crisis #2
- Supergirl (Volume 5) #5
- Supergirl (Volume 5) #16
- Supergirl (Volume 5) #24
- Supergirl (Volume 5) #30
- Action Comics #869
- Supergirl (Volume 5) #35
- Supergirl (Volume 6) #0
- Supergirl (Volume 6) #1
- Worlds' Finest #0
- Earth 2 #1