Renee Montoya, a police officer and detective of the Gotham City Police Department, was created for the animated series, but actually appeared in the comics first due to the lengthy production time of the show. She guest starred in numerous Bat-Family titles before being cast as one of the lead characters in Gotham Central, then 52. She also wore the mantle of The Question for a time.
Lock-Up also made the leap to The DCU in the New 52, surprisingly before Harley.
Roxy Rocket is a recursive canon immigrant — she originated in The Batman Adventures comic based on the animated series, then made it into the series, before finally migrating from the series to the DCU proper as an enemy of Batgirl.
Sewer King, also from the animated series, appeared in 52. He appeared in one issue, only to die at the end of said issue.
There's Raven, Jay and Lark, the Penguin's henchwomen from the DC Animated Universe. Lark was adapted from the comics while Jay and Raven were original characters, and it wasn't until the New 52 reboot that they were made canon.
The weirdest example is Condiment King: a throw-away joke villain... who got added to the DC Universe as a throw-away joke villain, only this time he really was a villain (his one DCAU appearance had him Brainwashed and Crazy rather than evil).
Veronica Vreeland originated in the animated series and finally made her first mainstream DC Universe appearance in the 2018 DC's Beach Blanket Bad Guys Summer Special one-shot. Prior to that, she also showed up in the out-of-continuity Batman: White Knight mini-series.
Terry McGinnis was seen in a few issues, but these were all set in the DCAU continuity (this includes his mini-series). As of Batman #700, however, he's been inserted in the main DCU timeline as both an alternate universe Batman, and in the main universe as a possible future successor to Damian Wayne. Damian in this case fulfills the role Bruce did in the DCAU. Another version of Terry showed up in Futures End. This one had been mentored by Bruce in a Bad Future, and had travelled back in time to the period of Futures End to try and Set Right What Once Went Wrong.
Likewise, Derek Powers was a Corrupt Corporate Executive from Batman Beyond who ran a company called Powers Technologies. Scott Snyder made the Powers family and their company canon in his Batman run, with Geri Powers, Derek's ancestor, acting as a supporting character. Derek himself eventually appears in a Gotham Academy annual, where he travels back to the present in an attempt to murder Warren McGinnis, the young boy who will eventually grow up to be Terry's father.
In a split between this and the Expy trope, Gotham Academy also introduced a young girl named Katherine Karlo, who eventually turns out to be Clayface's "daughter" (that is, a piece of his body that gained free will). She is the DCU's version of Annie, a one-shot character from The New Batman Adventures with the same basic backstory and premise, in all but name, though given that Clayface is named Basil Karlo, it may have been a bit more obvious the connection this time.
Nora Fries, Mr. Freeze's cryogentically frozen wife. She was created for Batman: The Animated Series and then imported into the comics in Batman: Mr. Freeze #1, as was Ferris Boyle, the Corrupt Corporate Executive who caused the accident that transformed Victor into Mr. Freeze. Even Batman & Robin used Nora as a plot device. The addition of Nora and her tragic story had a massive impact on Mr. Freeze's popularity; prior to his appearance in the cartoon, he hadn't shown up in comics in almost 20 years.
The DCAU interpretation of Clock King, who was originally a Green Arrow villain, made the jump to the comics as a Batman foe. A character with the same name and time motif had appeared on the 60s Batman (1966) TV show.
The Grey Ghost from Batman: The Animated Series eventually appeared in Batgirl, only to be killed off in one of the final issues. He showed up again post-New 52 in Gotham Academy as the school's drama teacher.
When Batman: The Animated Series's version of the Matt Hagen Clayface's backstory was ported over in DC Rebirth for its version of Basil Karlo's Clayface, so did Roland Daggett and his role in Clayface's origin.
Summer Gleeson is mentioned by name in the No Man's Land series.
The 1960s TV series
Batgirl is an interesting case. The character was created by DC Comics in 1966, at the behest of Batman (1966) TV-show producer William Dozier. Technically, she appeared in the comics (just barely) before her first broadcast appearance — but she exists only because the television show wanted an "official" young female character fighting alongside Batman and Robin.
King Tut from the Batman (1966) TV series appeared as the main villain in a story arc of Batman Confidential, giving him Canon Immigrant status some 40-something years after he first appeared. King Tut also makes an appearance in Batman: The Brave and the Bold, which makes him an immigrant from one TV canon to another.
Brave and the Bold also went one step further, having cameos by the likes of Louie the Lilac, Bookworm, The Archer, Marsha Queen of Diamonds, The Siren, Ma Parker, Black Widow, Shame and Egghead. All had a cameo in a prison break, in one episode. All of them were villains created specifically for the '60s TV series.
Egghead made the jump to the DCU as well in Gotham Academy, though looking less like Vincent Price.
Bookworm first officially made the jump to the comics in a 1989 Huntress story that saw him killed off. He returned in the New 52, where he's the school librarian in Gotham Academy.
The Arkham game series
The new, female Copperhead was created for the video game Arkham Origins, but was announced to be coming to the New 52 before the game was even released. However, due to nixed plans, her comic debut happened long after the game's release as part of DC Rebirth.
Detective Comics #1000 introduces the Arkham Knight from the video game of the same name into the DC Universe. However, rather than being Jason Todd like in the game, the comic version of Arkham Knight turns out to be Astrid Arkham, the daughter of Jeremiah Arkhamnote This potentially also makes her a Composite Character with Lady Arkham, a female supervillain in the Arkham family whom was the main villain of Batman: The Telltale Series.
Lord Death Man from the 1960s Batman manga appeared as a villain in Grant Morrison's Batman and Batman '66, making him an immigrant to two continuities. (Death Man actually first appeared in the sixties comics; the stories in the manga version were mostly taken directly from the western counterpart, although they were expanded upon greatly and japanified.)
The same is true of the other Bat-Manga villain who cameos in the Lord Death Man story; Professor Gorilla is loosely based on "the Living Beast-Bomb" from Detective Comics #339.
Carrie Kelly was first introduced as the new Robin in Batman: The Dark Knight Returns, but during the New 52, she appeared in the mainstream continuity as Damian Wayne's drama tutor. She wore the Robin outfit to a costume party as a Mythology Gag, but thus far there's been no indication she'll actually become a costumed hero in this continuity.
Chase Meridian was created for Batman Forever as Bruce's new love interest and a Gotham psychologist who worked with the police. Years later, she was brought into the DC Universe via the Legends of the Dark Knight digital comic, which established her as a psychiatrist who worked at Arkham.
Richard Sionis, a proto-Black Mask who also appeared in Gotham, is established as a previous Black Mask in the Rebirth comics as well, being the father of Roman Sionis.
Following the unexpected departure of Ruby Rose from the Batwoman TV show, the writers created a new Batwoman named Ryan Wilder to take over as the protagonist of the series. Prior to the airing of Batwoman's second season, DC introduced Ryan into the comic continuity in the aftermath of The Joker War, with a cameo in Batgirl #50. It appears increasingly unlikely that Ryan will follow her show counterpart, however; as of July 2021, she herself has reappeared only once note In Batman: Urban Legends #5 as a hooded supporting figure whose signature is a combustible red card (leaving Oracle to dub her a wildcard), Kate Kane still operates as Batwoman with no reason to give it up or otherwise leave, and Kate was shown to still be Batwoman in the potential future of DC Future State.