It is not legal to download the Android operating system for free unless it is provided directly by its creators, Google. Android is an open-source operating system that is licensed under the Apache License. This means that it can be modified and distributed by anyone, but with certain restrictions. In most cases, downloading Android from an unofficial source is considered piracy and violates copyright laws. Additionally, downloading an unofficial version of Android can pose a security risk as it may contain viruses or malware that can harm your device. It is best to obtain Android from official sources, such as the Google Play Store or directly from the website of the device manufacturer.