Like with Pokémon's previous iterations, this game has numerous important people throughout the game who will aid you on your journey.

Name Rater

Location: Castelia City

In the Pokémon Gym road of Castelia City, there is a man in the lefthand building who will change your Pokémon's name. Like the Name Rater of the previous games, he will only change the names of Pokémon you have captured. Pokémon obtained in trades cannot have their names changed. Pokémon captured and labelled as N's Pokémon also cannot be named
Massage

Location: Castelia City

In the Pokémon Gym street of Castelia City, when you enter the building opposite to the Gym, you will find a character who will give your Pokémon massages. These massages increase your Pokémon's happiness and you can give one a day
IV Checker

Location: Nimbasa City

In the Gear Station, you will find a guy who will judge you based upon your Pokémon's Individual Values. He will tell you which stat is the best stat of your Pokémon and will then tell you how good it is, saying if it's Decent, Very Good, Fantastic or Can't be Better.
Move Relearner

Location: PWT

The Move Relearner is located within PWT and is done by a girl in the leftmost stand and is willing to teach your Pokémon any of the moves in its level up learnset that it has previously forgotten. For some Pokémon, this is the only way you can get some of the moves. This however, is not free, and costs you one Heart Scale per attack.
Move Deleter

Location: PWT

The Move Deleter is also located in the PWT, to the east of the Move Relearner. This character will delete any more off of your Pokémon, including any HMs that were taught to the Pokémon. There is no charge for this
Kanji Change

Location: Floccesy Town

On Japanese games, you have the ability to switch the text from Katakana to Kanji at will. Simply chat to this trainer by the clocktower in Floccesy Town and she will change it for you
Happiness & Effort Values

Location: Everywhere

If you call up Bianca on the Xtransceiver, she will offer you the opportunity to check to see the Happiness of your Pokémon. She will give statements based on how happy they are and will offer tips to improve it. In addition to that, she also provides a function of checking for Effort Values and letting you know if you have filled them. You can also check happiness in Icirrus City's Pokémon Fan Club
Statement Happiness Values
What great friends you are! It's so nice how you trust each other! It makes me kinda jealous! 250+
You two sure get along great! It looks like you are having fun being together! You seem bright and cheerful! 200-249
You're starting to get to be friends. Just maybe, walking along the same path has made you understand one another. 150-199
You still have room for improvement. How nice! I mean, you can become even better friends!. 100-149
You aren't getting along, are you? It's glaring at you with a look that's kinda scary 50-99
You aren't getting along, are you? It doesn't look like it's having fun even when you're together 0-49
Type Combatibility

Location: Everywhere

If you call up Cheren on the Xtransceiver, he will offer you tips on what your Pokémon are weak to, their moves and their abilities.
Legendary Locations

Location: Everywhere

If you call up your RIval on the Xtransceiver, he will tell you the locations of some weird places which end up being the locations of various Legendary Pokémon.