X had no single "game director" but had one event director (Motomu Toriyama), one map director (Takayoshi Nakazato), one battle director (Toshiro Tsuchida), as well as a heavily involved producer (Yoshinori Kitase).
http://en.wikipedia.org?search=%22Ultimania+development%22&ns1=1 ^Almost all FF Ultimania interviews ever. Tons of exclusive info.
As much as he seems to get the negativity these days, I would have to say Kitase. I know everyone's opinions vary heavily, but the vast majority/public tend to favor FFVI for old school purists, FFVII for the PS1 crowd, and FFX for the PS2/PS3 era, two of which he directed (VI and VII) and one of which there was no lead director but he played a huge role as an actively involved producer (X).