A Doubting Thomas is someone who will refuse to believe something without direct, physical, personal evidence; in other words, a skeptic.
Famous quotes containing the words doubting and/or thomas:
“Still let us not be over-sanguine of a speedy final triumph. Let us be quite sober. Let us diligently apply the means, never doubting that a just God, in his own good time, will give us the rightful result.”
—Abraham Lincoln (1809–1865)
“A friend to all is a friend to none.”
—18th century English proverb, collected in Thomas Fuller, Gnomologia (1732)