Boston--John Hancock Mutual Life Insurance Co. has named David D'Alessandro CEO. He will assume the title effective June 1, 2000, replacing Stephen Brown, who will retain his chairman title and assume a more active role in the company's retail mutual fund business. Mr. D'Alessandro is currently president and chief operating officer. He will oversee all of John Hancock's businesses, including its institutional pensions operations. John Hancock has more than $131 billion in institutional and retail assets under management. Mr. D'Alessandro rose through the public relations and marketing ranks to Hancock's top spot.