Complex sentence: O'Brien was born in Brookline, Massachusetts (a suburb of Boston), to Thomas O'Brien, a physician, epidemiologist, and professor of medicine at Harvard, and Ruth O'Brien (née Reardon), an attorney and partner at the Boston firm Ropes & Gray.
Split into simpler sentences: O'Brien was born in Brookline, Massachusetts (a suburb of Boston). His mother, Ruth O'Brien (née Reardon), is an attorney and partner at the Boston firm Ropes & Gray.