It would be 3 Hokage Sarutobi, Databook 4 confirmed what was said in part 1 :
Databook 4 says he knows all 5 nature elements , all ninjutsu and genjutsu in Konoha and it also specifically mentiones hiden ones like Nara or Akimichi clan jutsus which Hiruzen can perform.
He is only one in...