Ookido Hakase
Ookido Hakase is Shigeru's grandfather and the world's leading Pokemon Professor. Before Shigeru started on his Pokemon journey, Ookido could have taught him a lot about Pokemon and also gave him training tips. After all, Ookido used to be a trainer himself, yes?

Ookido could have also urged Shigeru to become a master. As a pastime, he and Shigeru used to place bets on Satoshi, one being a bet of one million dollars if Satoshi caught a pokemon before reaching Viridian. Ookido lost, and Shigeru was suddenly very rich. Perhaps that is how he could afford that red convertible.

May
May is Shigeru's older sister. She seemed very supportive of him, but however, she also seemed to encourage Satoshi more than her own brother.