Is it a Butler's Friend or an Ah-so?

I own an old cork puller that consists of two thin springy prongs that slide down the sides of a cork so that the cork can be removed undamaged. I’ve always thought it was called something like an ‘Ah-So’. A friend told me it is actually called a ‘butler’s friend’. Which is correct?

We have also heard the name ‘Ah-so’ mentioned, but the traditional name is indeed ‘Butler’s Friend’—and for an interesting reason. It is said that dishonest butlers would use it to open a bottle of wine without marking or damaging the cork. They could then enjoy the bottle’s contents, replace it with an inferior wine, then reseal the bottle—all without the lord of the manor knowing about it.

Frankly, if the lord of the manor couldn’t tell the difference, he probably deserved to lose his good wine.