Yahweh.
God´s real name is Yahweh but Elohim, Adonai, Jireh, Shadai, Tzevaot, El Elyon and Abba are also very popular and important in christianity.
Of course Allah is also a real name of god in Islam and there are people believing that Bhudda is god.

It is also interesting to be thinking about the translated versions of the word god as for example Gott (German), Gud (Swedish & Norwegian), Dieux (French), Dios (Spanish) Dio (Italy), Kami Sama (Japan), Prah Jau (Thai), Bog (Russia & Poland), Patmeshwa (Hindi), Shangdi (Shen) (China) and Jumala (Finland) and of course Theos (Greek).

Jehova has also become a popular name of god.

Some eastern religions consider Vishnu and Rama real name of god. Maybe Shiva...
Gods real name is Yahweh
Gods real name can be different in other religions
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