Sage isn't a person. It is a title. It is a name for a leader of Team Plasma. There are seven of them and their names are Ghetsis, Rood, Zinzolin, Gorm, Giallo, Ryoku, and Bronius.
Each of the sages give out a different TM before being arrested by the looker. The TMs that they will give out are:
-Ghetsis gives you nothing
-Gorm gives you TM75 swords dance in the dreamyard
-Bronius gives you TM69 rock polish in chargestone cave
-Rood gives you TM32 double team in route 18
-Zinzolin gives you TM01 hone claws in cold storage
-Giallo gives you TM08 bulk up in route 14
-Ryoku gives you TM04 calm mind in relic castle
Note: you can only get these TM's after you defeat the Pokemon league, N, and Ghetsis.