Leventhal was a key figure in the transformation of Southern California after World War II as the region grew into a densely populated metropolis. His firm, Kenneth Leventhal & Co., guided such prominent real estate developers as Ray Watt, Trammell Crow and Donald Trump through times of expansion and financial distress.
Leventhal was a leader in the specialization of the accounting profession, longtime partner Stan Ross said.
"He thought an accountant had to be more than just an accountant," Ross said. "We were on the outer edge of accounting, tax and other issues that affected the real estate industry so we could provide them with strategic consulting that would enable a company to increase their growth."
Leventhal and his wife, Elaine Otter Leventhal, started Kenneth Leventhal & Co. in the second bedroom of their Los Angeles apartment in 1949. A chance meeting with Watt at a business luncheon drew Leventhal to real estate, and as he began to recruit partners, he pushed them to become experts in the field.
In 1961 he lured Ross from New York, and the pair became one of the best-known duos in the real estate industry. Early clients included home builders Watt and William Lyon. In a mid-1970s bidding war for the Irvine Co., Leventhal's firm successfully represented major real estate developers including Alfred Taubman and Donald Bren.
One of his tools in the $282-million deal for the Irvine Co. was a computer, which Leventhal considered a secret weapon at the time. "In the next 30 years, the computer is going to become even more important as its sophistication grows," he told The Times in 1979.
Until that that time arrived, accountants completed complex transactions using slide rules, adding machines and pencils, Ross said. "You did a lot of rounding up or down to structure a deal."
Leventhal was born May 28, 1921, in Cincinnati to Rose Belle and Julius Leventhal. The family moved to Los Angeles when he was 8. Soon thereafter he became a carrier for the Herald-Express, an afternoon newspaper.
In talking with his boss, he learned that the man planned to take a correspondence accounting course and go into business for himself. All it took to get started was a pencil, his boss told him.
"I figured that for a nickel, I could be my own boss," Leventhal said later, "and I never changed my mind."
After serving in the Army during World War II, he attended UCLA on the G.I. Bill. There, he met and married a classmate, Elaine. The accounting firm they founded grew into one of the largest in the country as it discovered ways to prosper in both the highs and lows of real estate cycles.
When some of its clients ran into financial difficulties during downturns in the economy and property markets, the firm began to help them reorganize outside of Bankruptcy Court. It built a reputation as a workout specialist, advising companies in complex reorganizations, including some of the biggest names in U.S. real estate, among them Trump, hotel developer John Portman, and mall developer Edward DeBartolo.
It also advised the federal Resolution Trust Corp. in selling billions of dollars of real estate owned by failed financial institutions during the early 1990s. As its reputation grew, the firm took on global assignments, advising international clients in restructuring and selling portfolios of distressed real estate and other assets.
By 1995, when it merged with Ernst & Young, Kenneth Leventhal & Co. ranked as the ninth-largest certified public accounting firm in the country and had 13 offices nationwide. Its affiliate, Clark Kenneth Leventhal & Co., was the 12th-largest accounting firm in the world.
"Ken Leventhal was one of the giants on whose shoulders we now stand," said William W. Holder, dean of the USC Elaine and Kenneth Leventhal School of Accounting.
Leventhal is survived by his wife, Elaine; his brother, Henley; his sons, Robert and Ross; and a granddaughter, Emma.
Services will be held at 2 p.m. Thursday at Mount Sinai Memorial Park in Hollywood Hills.