A leading figure in modal logic, Professor Segerberg was emeritus at Uppsala University, where he had held the Chair in Theoretical Philosophy from 1990 until his retirement in 2001.  The Uppsala memorial notice is here.  (Professor Matti Eklund at Uppsala tells me that some remembrances will soon be posted htere as well.)  Comments are open here for remembrances from those who knew Professor Segerberg or for those who would like to comment on the significance of his work.