A free app for Android, by The Simple Apps.

File Locker is an application that allows you to lock private files and folders on your device, so that no one else can access them. It works as a simple password lock, with a pattern, a PIN, or a fingerprint, and it can also work as a security token, if your device supports fingerprint authentication.

File Locker can also lock videos, images, audio, and documents. 

File Locker works as a simple password lock, with a pattern, a PIN, or a fingerprint, and it can also work as a security token, if your device supports fingerprint authentication.

If you forget your password, you can clear app data or re-install app to reset password.