he is in jublife. if i am wrong someone else will provide an answer
in diamond and pearl you find him in Eternacity
happiny
He is the Daycare Guy- he takes care of your Pokemon for a small fee
Happiny
go to the Pokemon league and get a job
You finish the Pokemon league and get the national pokedex You finish the Pokemon league and get the national pokedex
Define 'gray guy', there are lots of special characters in Diamond
He is in Eterna city there is a big buildig next to the pokemart and then you will see a old man wearing blue and has white beard! ;)
The name of the "yellow haired" guy is Barry if you are talking about Pokemon diamond and pearl series.
In pastrana city there is a guy who teaches Pokemon moves back that your Pokemon forgot.Ö®
go to solaceon town and left of Pokemon center
go iside the house and talk to the guy