Again, you are referring to 神武天皇 (じんむ‐てんのう, Jinmu Tennō) or 崇神天皇 (すじんてんのう, Sujin Tennō), both were the legendary (if I am not mistaken) rulers of Japan; first one often referred to as 始馭天下之天皇, and the other as 御肇国天皇. 始馭天下之天皇 has the same meaning as 御肇国天皇, whereas 肇国 alone means "a founding state", and you read it as I said in my previous post. はつくにしらす (御肇国知らす) that you are talking about means "the first ruler of the nation", and it is NOT a name of any of the emperors per se.