Um...

It is "formed" by plotting the Gx value as the X-coordinate and the Gy value as the Y-coordinate on a Cartesian plane.

If you are asking who chose those values for the base point in the secp256k1 curve, and why, then I believe they were chosen by the Standards for Efficient Cryptography Group. I don't think they specified exactly how they came up with that particular point for the base point.

If you are asking who decided that bitcoin would use the secp256k1 curve, and why they chose that curve, the secp256k1 curve was chosen by Satoshi Nakamoto, and he didn't specify why he chose that curve.