William Johnson McDonald (December 21, 1844 – February 8, 1926, though some sources give his date of death as February 6 ) was a Paris, Texas banker who left $850,000 (the bulk of his fortune) to the University of Texas System to endow an astronomical observatory.

[2] The bequest was unexpected, and his will was contested, but after prolonged legal disputes the university received the money.

The McDonald Observatory is named after him, with Otto Struve becoming the first director.

As a young man, he was a private in the Confederate Army.

[1] He became wealthy through his businesses as a lawyer and a banker, but remained frugal his entire life.