|You need a modem. |
You don't need a router.
However, a router is a darn good idea as they help to prevent intrusion and allow you to have multiple computers access the internet through a single external IP address.
Some providers use combo devices that are a modem, a router and a wireless access point all combined into one device.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.