A child born from a mortal and a God/Goddess is called demigod. Demigod were also known as half god and half mortal. The English term "demi-god" is a calque of the Latin word 'semideus' or "half-god".

An immortal demigod (-dess) often has tutelary status and a religious cult following, while a mortal demigod (-dess) is one who has fallen or has died, but is popular as a legendary hero in various polytheistic religions. Figuratively, it is used to describe a person whose talents or abilities are so superlative that they appear to approach being divine.

There were many demigods and the first was Dionysus. Dionysus was born from a mortal woman Semele and Greek God Zeus. Dionysus eventually became the god of the grape-harvest, winemaking and wine. The most popular ones are Hercules, Achilles, Hanuman.

More Info: en.wikipedia.org