Mortimer Caplin, who as Internal Revenue commissioner in the early 1960s was credited with making taxpaying more tolerable for the majority of Americans who do so voluntarily and tougher for the rest to avoid or evade, died on Monday at his home in Chevy Chase, Md. He was 103.

His death was confirmed by his son Lee.

Mr. Caplin pursued tax cheats who were costing the government billions of dollars. He persuaded Congress, despite the opposition of corporate America, to require that expenses of more than $25 be itemized if they were claimed as tax deductions.

“The hunting lodge, the yacht, the safari, they’re going to be out,” he told Time magazine for a 1963 cover article. “But I can see $24.95 specials developing all over the country.”

Mr. Caplin also introduced a centralized computer system — known as the Martinsburg Monster, for the city in West Virginia where it was located — to audit returns swiftly and equitably. Revenue and compliance increased as a result.