Although the bulk of the Pokemon anime focuses on Ash overcoming his own flaws as a trainer and gaining new strength and allies, he is also constantly accosted by villains in his journeys, some more memorable than others. While some of these villains are based on their video game counterparts, others are created just for the series and only appear a handful of times in Ash's adventures.

Related: 10 Super Weird Pokemon Fan Games That Are Worth Checking Out

There are some, however, that left such a lasting impact following their appearance that many fans, even years after seeing them on screen, still remember their debut episodes and how they affected the course of Ash's life while also being some of the audiences favorite characters, despite them being the villains.

10 The Ultra Beasts

While not all Ultra Beast are malicious in their actions, it's hard to ignore the fact that they are an invading force that wreaks havoc on the Alola region and force a group of school-aged children to put them in their place. While several Ultra Beasts caused problems for Ash and his friends, such as the multiple Guzzlord that the group had to deal with, none are quite as villainous as Nihilego, which not only tried to kidnap Lillie multiple times but took over Lusamine's body and attacked Ash just because they could.

9 Lysandre

Lysandre as he appears in the Pokemon X & Y games may be a little forgettable, with the exception of his final battle outfit, he was given much more room to grow in the anime that made him a more memorable character. Aside from keeping his obsession with destroying the world to keep it beautiful, his team also got a significant upgrade that allowed him to nearly defeat Ash, despite his team at the time being one of the strongest he had ever had. The most notable update to his character, however, is the fact that his Mega Gyarados is now shiny, a variation that has only been seen elsewhere with Lance's Gyarados.

8 Guzma

Unlike Lysandre, Guzma was an interesting character both in video games and in the anime. After having a longstanding rivalry with Professor Kukui, Guzma was sick of constantly losing in battle and strived to become a better trainer alongside his partner, Golisopod, who was not only a very powerful Pokemon but was also the source of some of the best battle in the series.

Related: Pokemon: Every Pokemon The Main Characters Caught In Pokemon - Indigo League (& Who Caught Them)

While Guzma isn't as villainous in the anime as he was in the video games, he is present to be a thorn in Ash's side on multiple occasions, which comes to a head in the Alola League, where he faces off against Ash in a two vs two battle that culminates in Ash finally defeating Golisopod.

7 Cyrus

Before Cyrus's story was expanded upon in Pokemon Platinum, he wasn't the most memorable of video game villains and was simply there to annoy the player most of the time. After his story expansion and his appearance in the Pokemon anime, however, this all changed and he has gone on the become one of the best villains in the series. Aside from potentially succeeding in his goal to build a utopian world in the Distortion World, something few other villains can brag they have done, he was also able to gain control over the three Lake Guardians, Dialga, and Palkia before his disappearance, a feat that few other characters have been able to replicate.

6 Team Galactic

Cyrus may have been the leader of Team Galactic, but his underlings were just as memorable as he was in the anime. Aside from appearing multiple times to cause trouble, several key members of Team Galactic would have their own rivalries with Ash and his group, including Saturn's Toxicroak's ongoing rivalry with Brock's Croagunk, while also causing some major issues for the people of Sinnoh, including taking control over the Steel-type Pokemon of Iron Island that was only stopped by the timely intervention of Ash and his allies.

5 Ghetsis

Of all the Pokemon villains in the series, none are as loved by fans as Team Plasma and Ghetsis, as they are one of the few villainous teams in the series with an understandable goal that, at least on the surface, isn't simply about controlling the world through Pokemon. That being said, even once Ghetsis reveals that his plan is essentially the same as all other evil teams, he is clearly more capable, though much more unstable, than the majority of other evil team leaders.

4 Hunter J

Appearing in a handful of episodes in the Sinnoh series, Hunter J is a bounty hunter of sorts that captures Pokemon to sell off to the highest bidder, even if that Pokemon is already partnered with a trainer. While she was shown to simply be a dangerous bounty hunter at first, she would eventually work with Team Galactic in order to capture the Lake Guardians for their own purposes.

Related: Pokemon: Every Pokemon That Evolved In Pokemon - Indigo League

Hunter J is also notable for being one of the few characters in the Pokemon anime who may have died, as she was last seen trapped inside her plane and sinking to the bottom of Lake Valor after being attacked by Uxie and Mesprit. Since she hasn't appeared in the series since this episode, it is unknown whether or not she survived the encounter.

3 Malamar

When Malamar was first introduced in the Kalos series, it appeared that it was simply being used for the evil purposes of an unknown individual. In a twist that many fans didn't see coming, the Malamar was actually the mastermind and was simply controlling its "trainer", Madame X, in order to take over the world. This is one of the only times that a Pokemon was shown to be evil in the series, as, in nearly every other instance, the Pokemon were simply a tool used by a trainer.

2 Giovanni

Giovanni doesn't get anywhere near as much character development in the anime as he does in the video games, but that hasn't stopped him from being a truly great villain. Aside from being able to stay relevant when every other evil team in the series has fallen apart, Giovanni has spread Team Rocket's influence all across the world, though not always successfully. His greatest accomplishment, as short-lived as it was, was the creation of and control over Mewtwo, though, thankfully, this didn't end well for him and he hasn't attempted something similar since.

1 Jesse and James

First appearing in the second episode of the series, Jesse and James have been a thorn in just about everyone's side for many years. Aside from having a strong commitment to capturing Ash's Pikachu, they have shown that they are very capable when it comes to Pokemon battles and contests, as well as just about any other non-villainous job that they can find. Ironically, this pair of criminals are better than Ash at just about everything, so long as it doesn't involve working for the bad guys.

Next: 10 Shiny Pokemon That Look Worse Than Their Normal Versions