Gilgamesh, the original epic mount.

I dare say THIS ought to knock him dog a peg or two.

I do not appreciate this artwork.

hahahaha, this is made of pure WIN

I appreciate this artwork.

I appreciate this. I knew Saber always wanted to RIDE Gil

Saber only has a Rank B in riding. I call shenanigans.

So... now You can Summon Arturia in Rider-class!
Half of tha mana usage!

Hurry! Don't let anyone summon Rider Arturia before you!

Tetsamaru said:
Saber only has a Rank B in riding. I call shenanigans.

So? All that means is average skill rather than mastery and no phantasmal creatures; Gil is part human, so he's eligible.

All hail the king of mounts

Gil: "I never knew she was into this sort of stuff!"

I'll be over here laughing like a madman.