Fifteen years ago, Bruce Timm ended his lengthy animated universe with Justice League Unlimited. After introducing audiences to Batman, Superman, Wonder Woman, Flash, Green Lantern, Hawkgirl, and Martian Manhunter, Timm and his team decided to bring just about every character in the DC universe together in one show.

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Now, in honor of the shows 15th anniversary, we decided to take a look back at the ten best episodes from one of the most iconic Super Hero series of all time.

10 The Great Brain Robbery

In an attempt to find where Gorilla Grodd (Powers Booth) is located, Dr. Fate, Mr. Terrific, and Green Lantern convince the Flash to use his mind as a way to locate him. While this is happening, Lex Luthor is using a mind-reading device to read Grodd's mind and find a way to bring Brainiac back. An error occurs, causing Lex and Flash to swap minds. What makes this episode great is the tension it creates and the meta-humor. While Flash is in Lex's body, you can tell that the Secret Society is starting to get smart on what's happening. Meanwhile, Lex is slowly able to outmatch the Justice League with his intelligence and the Flash's powers.

It makes for some robust action and great humor. The big laughs come from hearing the VO's play opposite of what they're used to. Hearing Clancy Brown add some youth and confusion to Lex leads to some great moments, as is hearing Flash's VO combining suave and intellect to the Flash. It's even funnier when you remember that the voice of the Flash, Michael Rosenbaum, also played Lex Luthor in Smallville.

9 The Once and Future Thing

What would happen if you crossed Justice League with Back to the Future?  You get "The Once and Future Thing." When the dweeby scientist Chronos (Peter MacNicol) is fed up with his life and nagging wife, he builds a time machine to make his life much better. While doing this, he inadvertently begins to tear the Time-Space Continuum. It's up to Batman, Green Lantern, and Wonder Woman to save the day and the universe.

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Along the way, they team up with Jonah Hex, Pow-Wow Smith, an elder Static, and Batman Beyond. The action is great, the story is all kinds of fun (with a few dark moments sprinkled in between), and seeing our heroic trio interacting with past and present heroes is a delight.

8 Dark Heart

When an alien superweapon arrives on earth, the Justice League gather as many members as possible to stop it. Despite a relatively straight forward story, the episode more than makes up for it with a plethora of great action sequences.

The best way to describe this episode is what would happen if a child took all his Super Hero action figures and threw them against other toys. From a scene where Batman is fighting robots with two large Batarangs to one with Superman, Wonder Woman, and Steel attempting to get close to the device, the episode has an amazing "Kids playing in the Sandbox" feel to it.

7 Flash and Substance

One of the more humorous episodes of JLU, "Flash and Substance" sees The Rogues (consisting of Mirror Master, Captain Cold, Captain Boomerang, and The Trickster) attacking Central City in an attempt to destroy the Flash. Luckily, Flash is backed by Batman and Orion.

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The appeal of this episode comes entirely from the Flash. While this version of the Flash(Wally West) has always been a jokester, seeing him take center stage and take on the Rogues is a fun change of pace. It also makes for some excellent action sequences. It even has some small Easter Eggs for Flash fans, including Mark Hamil reprising his role as the Trickster from the '90s Flash TV series.

6 The Return

A sequel to "Tabula Rasa" from Justice League, "The Return" sees the robot Amazo (Robert Picardo) coming back and seeking vengeance on Lex Luthor. When it seems that the Green Lantern Corp Has been destroyed, the Justice League attempt to combat the android. However, Amazo has grown so powerful; he's able to defeat every single member of the Justice League. Seeing Amazo overcome each member of the Justice League is both fun and haunting, but the real kicker is the person who ends up defeating Amazo is none other than Lex Luthor.

After having been diagnosed with cancer, Luthor has "turned over a new leaf" and decides to run for president. What's even more shocking is that Luthor doesn't win the battle with Amazo with weapons or fists, but his mind. It set the stage for how audiences and the league would see Lex Luthor for the next season.

5 Wake the Dead

After the events of "Starcrossed," the world hasn't seen much of Hawkgirl. When her old friend, Solomon Grundy, is brought back to life and goes on a rampage, the Justice League attempt to stop him. When they're not enough, Hawkgirl returns to the field with help from Dr. Fate and Amazo.

What makes this episode so impactful is just seeing Hawkgirl come to grips with what she did in "Starcrossed" while trying to move on with her life. She made mistakes, and not everyone is going to forgive her, but she's still a hero, and that's good enough for her. Sure, the action is excellent, but the most significant battle is often the ones that come from within.

4 Epilogue

When Batman Beyond was canceled, the series was never given a proper ending. With this episode, the show finally gives a proper send off to the futuristic version of Batman, Terry McGinnis. McGinnis, now an adult ready to propose to his GF, learns a shocking truth that ties into the legacy of Batman.

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Along with this intriguing storyline, we also get to see one of the darkest and most touching moments in the show. It's a moment that's up there with any of the best episodes of Batman: The Animated Series. It's a great send off to one of the most popular incarnations of Batman.

3 For The Man Who Has Everything

Based on the Alan Moore story of the same name, this episode sees Superman trapped in a mental prison that has him living a perfect life. While this is happening, Wonder Woman and Batman fight against Mongul (Eric Roberts) to free their friend. Much like the comic, the biggest draw is seeing what Superman's life would be like if Krypton was never destroyed.

Kal-El has married his childhood sweetheart, has a loving child, and works with his father Jor-El (Christopher McDonald), but he knows that this isn't real. While not quite as powerful as Batman: The Animated Series' "Perchance to Dream," "For the Man Who Has Everything" is a fascinating look at what could have been Superman's life and is just as enjoyable as the comic that it's based on.

2 Destroyer

As the series' final episode, Justice League Unlimted went out with a bang. After Luthor's failed attempt to revive Brainiac leads to the resurrection of Darkseid (Michael Ironside), the Justice League and the Secret Society of Villains must join together to put a stop to him once and for all.

"Destroyer" offers everything you could want in a finale; action, unlikely alliances, excellent animation and writing, and the ultimate showdown between Superman and Darkseid. It's also another episode that once again shows that Lex Luthor, despite representing the worst humanity has to offer, is also its best hope.

1 The Cadmus Arc (Question Authority - Divided We Fall)

Throughout the early episodes of the series, Cadmus and Luthor prove to be the ultimate match for the Justice League. Cadmus not only creates the Ultimen and a clone of Supergirl but its leader, Amanda Waller (C.C.H Pounder), learns Batman's secret identity. Meanwhile, Luthor is able to turn the public against the Justice League and humiliates Superman. It all culminated in what many fans call "The Cadmus Arc."

In it, The Question (Jeffery Combs) learns of an alternate world were Luthor becomes President, kills The Flash, and nearly sends America into another World War...That is until Superman kills him and the Justice League become fascist dictators of the entire planet. These episodes have great animation, suspenseful storytelling, fantastic action sequences, and phenomenal dialog, thanks to the late Dwayne McDuffie. While it's cheating to put four episodes as number one, "The Cadmus Arc" is one of the finest pieces of Super Hero fiction of all time.

Next: The 10 Fastest Characters in The DC Universe That Are Not Linked To The Speed Force

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