Was Thomas a heinous unbeliever, made a fool of by Christ?

No, not by Christ.

Thomas wasn't present when Christ appeared the first time. And since Thomas was under orders to not believe any excited report about Christ being here or there (Matthew 24:23 & 26) Thomas bravely stood his ground. Right on, Thomas!

When Christ finally shows Himself to Thomas, He congratulates him for having seen Him, not for believing Him. Thomas believed Christ the whole time! He was just a bit skeptical about his comrades and their zeal. Which is always wise.