How can I run a program as a root user when my Ubuntu 15.04 machine starts up?

On Ubuntu 15.04 I have this file: /usr/local/bin/myscript (it’s a script I made).

If I run this command under my account, it will do what I need it to do as a root user: sudo /usr/local/bin/myscript

I now want to make /usr/local/bin/myscript run on machine startup, but as a root user (as if I was running the sudo command but without having to type any password). How is this done on Ubuntu 15.04?