While still in its early stages, Pokemon Mystery Dungeon: Legendary & Ancient Discoveries already has Loads and Loads of Characters. Some are more developed than others, and some are downright Troperiffic. You can see all of them here.
ScepsThe Hero of the story. When the mystery Pokemon appeared in his hometown and launched an attack on Palkia and Dialga, Sceps touched the meteorite-like residue. He then woke up as a Treecko with no memories, and eventually befriended and joined Team Pokesquad.
RyoA Riolu who serves as the leader of Team Pokesquad and Sceps' closest friend.
IronA hard-headed Aron who is a member of Team Pokesquad. Likes to complain.
MudA Mudkip who serves as a member of Team Pokesquad.
Other Major Characters
The Mystery PokemonThe main villain. His identity is unknown.
HoundoomThe guardian of the Darkness Orb. He works for the Mystery Pokemon.
MantykeMantine's son who was rescued from a dungeon by Team Pokesquad. The gift he gave them as a reward turns out to be the Feather of Life.
SparkyA Pikachu who runs the Summer Town guild. Like Sceps, he was once a human.
EmpoleonThe second-in-command of the Summer Town guild.
DrifblimThe leader of Team Darkshroud. Has an unfriendly rivalry with Sceps.
MurkrowThe leader of Team Commando. Despises Sceps.
The HonchkrowsTwo Honchkrows that serve as Murkrow's lackeys.
MightyenaThe leader of Team Darkhound. He and Absol are some of Team Pokesquad's best friends.
Other Guild Members
The KrabbiesA bunch of Krabbies that worship Empoleon. They think that he's the guildmaster of the Summer Town Guild, and get him to destroy the ice on their frozen home.