The Diablo 2 Wiki
The Diablo 2 Wiki archive is available for anyone looking for information on Diablo 2. All information here is pre-D2R but contains a lot of useful information that is still relevant. Updated sections for new D2R features can be found on the PureDiablo Diablo 2 section

Ethereal Merc

From Diablo 2 Wiki

Ethereal items are best used on Mercs since they won't lose any durability while the Merc has them equipped.