Equity Office Properties Trust President and CEO Timothy Callahan has resigned his position for "personal reasons," the company said today. The board of trustees appointed Equity Office Chairman Sam Zell to the position during the transition.

The board also appointed a transition committee made up of three trustees: Zell, Sheli Rosenberg, vice chair of Equity Group Investments LLC, and John Foster, previously co-CEO of Spieker Properties Inc. The committee will be responsible for finding a successor for Callahan.

Callahan, 50, joined Equity Office — the nation’s largest office REIT — in 1996. Previously, he served as executive vice president and CFO of Equity Group Investments Inc. He also has held positions as vice president of finance with The Edward J. DeBartolo Corp. in Youngstown, Ohio, and senior vice president of Chemical Bank in New York City.

Equity Office owns and manages 128 million sq. ft. of space in 22 states.