I understood that Diego is Spanish for the original latin/ Greek name Jacob,holds the heel, ( Iacobus, Iakobos, Jacobo, Jaime, Yago) which later morphed into a Hebrew name. Western cultures it often was changed to James, or Jacques.

In 1602, Sebastián Vizcaíno (1548-1624) was sent to map the California coast. He arrived with his flagship "San Diego". Vizcaíno surveyed the harbor and what is now Mission Bay and Point Loma, naming the area for the Spanish Catholic Saint St. Didacus (More commonly known as San Diego).