Brian S. O'Neil was named chief investment officer of the Robert Wood Johnson Foundation, Princeton, N.J. He will replace John Gilliam, who plans to retire by midyear. Mr. O'Neil will be responsible for investment oversight of about $8 billion in foundation assets. He previously was head of the funds management group at Equitable Life Assurance Society, New York. His responsibilities have been assumed by other Equitable staff members and he will not be replaced, according to spokesman Jeff Tolvin.