[prteja11]

Law 0 / A robot may not harm humanity, or through inaction allow humanity to come to harm.

This precedes the 3 laws.

Source: Isaac Asimov in Robots and Empire

[daveloyall]

Don't forget, when Asimov introduced this new law, those (few) robots that were governed by it also had a modified First Law: "...except when such action or inaction would conflict with the Zeroth Law" (paraphrasing). That got interesting, quick!