An Argentinian legal philosopher, and longtime member of the law faculty at the University of Buenos Aires, Professor Bulygin enjoyed an international reputation for important contributions to all aspects of jurisprudence (see a collection of his papers from OUP for a sense of the range of issues he worked on); his most famous and influential work was probably 1971's Normative  Systems.  I will add links to memorial notices as they appear.

On a personal note, I had the great honor of meeting him a number of years ago when he came to my lecture at the University of Torcuato Di Tella in Buenos Aires.   A great legal philosopher and a very gracious man.

(Thanks to Luís Duarte d'Almeida for calling his death to my attention.)

UPDATE:   An obituary in Spanish is here.