ATMA has a Mercenary Items tab that allows you to easily transfer items to and from your hireling as well as view their stats. You can mule items from them just as you would from your character's inventory. If you want to easily transfer an item from the mercenary to your inventory or vice versa, you can drag the item to the buffer, switch tabs, and move the item from there.

The Iron Golem space in the lower right shows the item used to create Iron Golems for Necromancer characters who have created them.