LastPass is one of those must-have apps for both Android and iOS. It’s a password manager that lets you save your login credentials in a safe, secure way. On top of that, it can help generate nearly impossible passwords for you to use on your accounts. It’s all controlled with a master password. It has cross-platform support (premium version only) so you can use it on computers, mobile devices, tablets, or whatever.
There are others, but LastPass seems to be one step ahead most of the time. Additionally, the premium version is reasonably inexpensive. You can also grab LastPass Authenticator to go along with it for added security.