The comic character of Deathstroke, an Anti-Villain with occasional touches of Anti-Hero, has been decomposed into two characters in the island flashbacks. His name, Slade Wilson, and better fighting ability go to an Anti-Hero mentor to Oliver. His mask and villainous nature, with slightly lesser fighting prowess, goes to Billy Wintergreen, Slade's butler in the comics and here his former partner. In Season Two, Slade eventually takes on traits of the latter, however, and becomes closer to the comic self.
Green Arrow's Evil Counterpart Merlyn becomes Tommy Merlyn and his father Malcolm Merlyn. Tommy initially served as a Red Herring before his dad was revealed as the Dark Archer.
Similarly, from the start, Oliver's Love Interest was Dinah Laurel Lance, the civilian identity of Black Canary, here depicted without her powers or vigilante identity (and going by her middle name). In Season 2, however, they introduced Black Canary (simply dubbed The Canary) as a separate Canon Foreigner character named Sara Lance, with Laurel later taking the identity after Sara's death. This actually makes her a double Decomposite; in the comics, Canary was a Legacy Character, with her mother being the original; her mother has appeared on the show as a non-vigilante (as far as we know), so this new Canary is basically also a Composite Character of both the original Dinah Drake Canary and Dinah Laurel Lance versions of the character. Then, just to be confusing, Laurel was later killed off and replaced by a new character named Dinah Drake, who has no relation to either Laurel or Dinah.
The show's version of Count Vertigo was initially introduced as a young American drug dealer known only as "The Count." After being killed off, he was succeeded by the middle-aged European criminal Werner Zytle, the traditional Count Vertigo in the comics.
In the comics and most media, Roy Harper is Oliver Queen's very first ally who was kicked out due to his drug addiction. In the show, the now Canon Immigrant John Diggle takes the role of Oliver's very first ally before Roy is even introduced while his drug problems were distributed to Thea Queen (pre-Season 1) and Laurel Lance (Season 2), though he technically had a drug problem on the show itself in the form of the Mirakuru. Also, Roy was the first Speedy who later took up the name Arsenal, while here he started off as Arsenal and the name Speedy was given to Thea Queen.
Mia Dearden in the comics is a teenage runaway who is adopted by Oliver, trains together with his son, Connor Hawke, and becomes the second Speedy. While the show has no exact counterpart of her, Ollie's sister Thea has the middle name "Dearden" and eventually takes the Speedy moniker (which is stated to be her childhood nickname). Much later, Season 7 introduces Mia Smoak, Ollie's daughter who is friends with Connor Hawke.
Shado appears in the show and is still an archer, but the main aspects of her character (namely being the black veil wearing Dark Action Girl who is the daughter of The Leader of a powerful group) is incorporated to Nyssa Al-Ghul. Additionally, the show gave her a twin sister who was suspiciously introduced a season after her death. Due to this, her role as the mother of Emiko Queen is given to a Canon Foreigner named Kazumi Adachi.
In the comics, Ray Palmer's Love Interest is Jean Loring. In the show, Jean Loring appeared in Season 2 as the Queen family's lawyer and friend and she belongs to the generation of the Queen's matriarch, Moira. When Ray shows up in Season 3, he mentions a dead fiancee named Anna. He then reveals in Legends of Tomorrow that Anna's surname is also Loring, though what exactly is her relation to Jean is not stated.
Oliver Queen's illegitimate son in the comics is Connor Hawke. Here, the child's name is revealed to be William Clayton while Connor appears in Legends of Tomorrow as a separate, unrelated character, whose father is John Diggle.
And then, the Arrowverse version of Connor Hawke becomes a Decomposite Character again in Season 7. The Legends version was John Diggle Jr., who assumed the identity of Connor Hawke. The Season 7 flashforwards reveal that Connor Hawke is a different character who is John Diggle's adopted son - who is actually the son of Bronze Tiger - while John Diggle Jr. becomes the second Deathstroke.
"Ra's al Ghul" is revealed in Season 3 as merely the title of whoever The Leader of The League of Assassins is, thus making it this by default.
In the comics, Adrian Chase is one of several people who took up the Vigilante mantle. In the show, Adrian Chase serves as the Big Bad of Season Five under the codename Prometheus, while Vigilante, though modeled after Adrian's comic counterpart, turns out to be Dinah's former lover Vincent Sobel.
The comics' Amazo is a Killer Robot created by Professor Ivo who can absorb superpowers. In the series, Amazo is a freighter where Ivo performs his experiments with the Mirakuru. In the Elseworlds crossover, however, a comic-accurate Amazo is introduced, as in, a robot created by Ivo who can absorb superpowers.
Earlier, the show split the Weather Wizard into two characters. The first is Clyde Mardon (who existed in the comics but wasn't a supervillain), and the second is his older brother Mark, who becomes the new Weather Wizard after Clyde is shot and killed in the pilot episode.
In Season 2 following the Heroic Sacrifice of S.T.A.R. Labs engineer Ronnie Raymond, his role in the Firestorm matrix is taken by Jefferson Jackson. In the comics, the second Firestorm is supposed to be Jason Rusch, who already appeared during the middle of Season 1. Also, Jefferson has some of Ronnie's personality traits from the comics that his TV counterpart doesn't display. Namely, he's a cocky former football star like the comic version of Ronnie, while the TV version of Ronnie is a more responsible engineer and Nice Guy.
In the comics, Hunter Zolomon is the civilian identity of the Supervillain Zoom. Zoom is the Big Bad of Season 2, while Hunter Zolomon is a separate character introduced as Jay Garrick's Earth-1 counterpart instead, Actually, this is a case of Lying Creator as Jay is an alias and Hunter is indeed Zoom.
Caitlin Snow is the civilian identity of Supervillain Killer Frost. In the show, she appears as one of Barry's allies and friends while Killer Frost is eventually confirmed to be her Evil Twin from Earth-2. However, Caitlin later begins to transform into Killer Frost anyway.
Deathstorm is Ronnie Raymond's identity when he Came Back Wrong. Just like Caitlin, he is confirmed to be his Evil Twin from Earth-2.
The female version of Doctor Light appears in Season 2, and while she sports a costume and solar powers similar to those of her comic counterpart, her secret identity turns out to be the Earth-2 version of Linda Park rather than Kimiyo Hoshi. Hoshi later appears in Season 6, but as as an assassin who wields a photon rifle and prefers Civvie Spandex to a proper costume.
Although Edward "The Rival" Clariss does appear in the third season, most of his defining attributes (serving as the arch-enemy of Jay Garrick, wearing a dark copy of Jay Garrick's costume, using a Velocity 9 drug) were given to Zoom.
The show's take on the New 52 Future Flash appears in Season Three, but his nature as an evil version of The Flash is given to Savitar, who is revealed to be his time remnant.
The show has an in-universe example with Cicada. In the comics, Cicada's secret identity was David Hersch. After XS changes history by helping Barry destroy the Thinker's satellite, the dark matter-infused shrapnel turns a different man, Orlin Dwyer, into Cicada, while Hersch appears as a small-time terrorist. Years into the future, his niece Grace becomes the third version of the villain, and has several things in common with the original comic character, including his Ax-Crazy personality and being personally responsible for a loved one's death.
In the comics, Pohzar is the Soviet Firestorm. Here, his civilian identity appears but Valentina Vostok, the Negative Woman from the comics, is the one who becomes the Soviet Firestorm.
In the comics, Rip Hunter's Love Interest is his Sexy Secretary turned fellow Time Master Bonnie Baxter. The show introduces a Canon Foreigner named Miranda Coulburn as his wife, while Baxter's more direct counterpart Eve shows up halfway through the series. Interestingly, both ladies have similar appearances and are also Time Masters (well, was in Miranda's case).
Mari Jiwe McCabe aka Vixen exists in the universe of the show, but because of scheduling issues with the actress who plays her, an alternate Legacy Character version of Vixen named Amaya Jiwe appears in Season 2. This version of the character turns out to be Mari's ancestor.
In the comics, Arlene Luthor is the mother of both Lex and Lena Luthor. In this series, Lilian is Lex's mother and his father's wife and another woman gave birth to Lena.
Cat Grant has an estranged, adult son named Adam Foster and a teenage son named Carter Grant. In the comics she had one son named Adam Grant, who wasn't as old as either of his TV counterparts when he died.
Mon-El's father is named Lar Gand. In the comics Lar Gand is Mon-El's real name.
In the comics, Clark and Lois eventually have a son named Jon (named for Clark's adoptive father Jonathan), who later develops powers and becomes a superhero in his own right. In the TV show, they instead have two sons: Jon, who is now a normal kid without any superhuman abilities, and Jordan (named after Jor-El, Clark's biological father), who begins manifesting Kryptonian powers and eventually undergoes training to become a hero.
