Saber's True Name is Toyotomi Hideyoshi, a warlord and former subordinate of Oda Nobunaga, who came to rule over Japan. It is known that Oda Nobunaga calls Hideyoshi as Monkey.
He and Nagao Kagetora makes a cameo from Tsukumo's perspective of Holy Grail War.
(Source: Type-Moon Wiki)
Content compiled by AnimeList.moe from publicly available sources.
