Also known as the Game Master, DM, or GM. This person who shall remain nameless is responsible for the world, characters, and mechanics that the players interact with. This person roleplays NPCs, controls the actions of monsters, and passes judgment on the each player's dice rolls.
This particular DM is more fond of character interaction than the usual "killing monsters and taking their stuff" model of Dungeons and Dragons. Instead of awarding Experience per monster killed and per quest completed, this person chooses to award Experience for campaign objectives and extra feats of achievement - whether they were accomplished through battle or not.
It's not clear why the DM chose to create a campaign setting based on colorful, magical ponies.
Twilight Sparkle's player is relatively new to tabletop roleplaying. She knows the rules very well, but she doesn't have much experience actually playing the game. Still, she's determined to make the most of this adventure, no matter how unusual it is.
Since this is her first campaign ever, she is very devoted to her first roleplaying character and adventuring party. She sees the other players as true friends that have bonded through the game.
Her acqaintanceship with the DM is a little more strained, though. She wants to be friends with the DM as well, but it seems like their roles as player and creator get in the way, and she isn't sure how to get past that.
No one really knows whether or not she's played this game before. All that's apparent is that she has a penchant for finding unusual solutions to problems - much to the DM's chagrin.
Even in the face of criticism, Pinkie Pie's player remains unwaveringly cheerful and curious. She seems to have embraced the pony setting without comment nor question.
She's a very principled person, however. It's hard to tell what those principles are, but if you cross them, beware.
Applejack's player has some experience, and she genuinely enjoys all aspects of the game. That said, she's been with a variety of DMs - some good, some bad. She's not afraid to call the DM out on mistakes.
She loves to metagame, but most of her insights come from knowing the people involved in the game - their habits and tendancies, their reactions and word choice. Playing poker against her is probably a bad idea.
That said, she has her moments of self-consciousness. The last thing she wants to be at the end of the day is a hypocrite who doesn't practice what she preaches.
Rainbow Dash's player is all about killing monsters and taking their stuff - classic D&D. This kind of setting repulses her, but she suffers through it anyway - there's the slightest chance it could be very, very awesome.
She seems to treat this campaign as a trial by fire - for Equestria, with herself as the fire. Knowing the world is technically still in development, she'll do everything she can to inject pure awesome into it.
Having played with Applejack's and Rarity's players before in previous campaigns, she knows that they can both bring the heat in combat when it comes to that. Rarity's player has always been more socially focused, but to Rainbow Dash's player, it feels like Applejack's player has gone soft in this campaign.
Rarity's player is probably the most experienced, but enjoys talking more than fighting in the game. She was actually interested in the setting when the DM proposed it, even though it was unusual.
Out of the group, she seems to have the most experience on the DM side of the table. The campaigns she ran tended to be complex and engaging, but light on combat.
She secretly loves TV shows about thieves, hackers, and grifters doing criminal things for heroic reasons. The DM is the only other person who knows this.
Completely new to tabletop gaming, and a player of few words overall. She had to get a little help in building her character sheet, but she's actually very invested in her character and the setting.
While strategy and tactics elude her sometimes, she seems to have a very firm grasp on player/character separation and other roleplaying concepts. It's possible she has acting or writing experience.
During breaks and downtime, she has taken to reading through the DM's collection of sourcebooks. Not for research or optimization purposes, but to read all the interesting setting descriptions and flavor text.
When Rarity's player had a moment of doubt about her character's arc, she decided to shelve the rogue for a little while and work with the DM to flesh out a slightly sidelined character. Luna's low level is explained by her being weakened by the Elements of Harmony, but she still commands a great deal of authority and power... in theory.