The board of American International Group Inc. has voted unanimously to make Robert Willumstad, former president of Citigroup Inc., the company’s chairman.

Willumstad, 61, will succeed Frank Zarb, who has served as interim chairman since April 2005. Zarb, in turn, succeeded Maurice Greenberg.

Zarb will continue to be an AIG director and a non-voting member of each standing AIG board committee, AIG says.

Willumstad was elected to the AIG board in January.

Before becoming an executive at Citigroup, Willumstad spent 20 years in operations, retail banking and computer systems at Chemical Banking Corp., New York.

Willumstad also is on the board of Adelphi University and of Habitat for Humanity International, Americus, Ga.

Morris Offit will succeed Willumstad as chairman of AIG’s finance committee, AIG says.

Michael Sutton will succeed Offit as chairman of AIG’s audit committee.