That distinction goes to George Owen, Boston Bruins defenseman. He had played football while in college and when he entered the NHL in 1928 he wore the same leather helmet that he had worn in college when playing football.
Zdeno Chara
Craig MacTavish.
The first Detroit Red Wing to wear a helmet was Larry Mickey. He began wearing a helmet during the 1959-60 NHL season, primarily as a safety measure after suffering a head injury. His decision to wear a helmet paved the way for other players to follow suit in prioritizing player safety on the ice.
Craig MacTavish was the last "bare-headed" NHL player. He retired after the 1996-97 season and is currently the head coach of the Edmonton Oilers.
Willi Plett, Brad Smith, Guy Lafleur
For a while he didn't have to, but then the NHL required the use of a helmet.
You can in-fact wear a full cage in the NHL. The reason why players do not wear a cage is because it obstructs vision.
Michael Cammalleri
fiber glass
Yes he was the last NHL player, playing without a helmet. See: http://www.oilersheritage.com/history/dynasty_players_craigmactavish.html
Derek Sanderson, a former professional hockey player, played during a time when helmets were not mandatory in the NHL. He famously chose not to wear one for much of his career, which was common among players of that era. However, he eventually did wear a helmet later in his career, especially as safety concerns in hockey became more prominent.
some NHL players started to wear them in 2009 so it's likely in 2009