He wasn't a big man in size but he was a man in power and intelligence and second only to Glinda the Good in all the mystic arts of magic.

Glinda had taught him, and the Wizard and the Sorceress were the only ones in Oz permitted by law to practice wizardry and sorcery, which they applied only to good uses and for the benefit of the people.
The Wizard wasn't exactly handsome but he was pleasant to look at.

His bald head was as shiny as if it had been varnished; there was always a merry twinkle in his eyes and he was as spry as a schoolboy.

Dorothy says the reason the Wizard is not as powerful as Glinda is because Glinda didn't teach him all she knows, but what the Wizard knows he knows very well and so he performs some very remarkable magic.

The ten I have mentioned assembled, with the Scarecrow and Glinda, in Ozma's throne room, right after dinner that evening, and the Sorceress told them all she knew of the plight of Ozma and Dorothy.
"Of course we must rescue them," she continued, "and the sooner they are rescued the better pleased they will be; but what we must now determine is how they can be saved.