English equivalent for the Persian proverb "The mountain just gave birth to a mouse"

I'm looking for an idiom or expression to describe a well-known person/ organization/ politician/ government whose achievements in a given situation are smaller than what they had claimed or promised to be.

We Iranians have a proverb that literally means

The (roaring) mountain just gave birth to a mouse!

Its etymology is like this:

Once a volcanic mountain started roaring, hissing, and bursting bubbles. The people were waiting to see what would happen after all those huge roarings and loud booms. Finally, the volcano activity stopped and the people saw just a tiny mouse came out of there! (rather than a monster that was expected to come). So they said mockingly:

"Heh! After all those huge roarings, the (big) mountain just gave birth to a (tiny) mouse!"

Notes:

• The (roaring) mountain -symbol for an apparently big(=important) and strong person-here is figured like a woman who is screaming and shouting while is delivering her baby.

• We use this proverb for mocking an important person/organization/ government, etc ironically when they have used broad advertisements or have spent much money or resources over doing something noticeable, but the result/ achievement is less noticeable than it was claimed or promised to be.

Is there any equivalent for this Persian proverb?

I just found "much ado about nothing"; would it convey the same connotation?

Solution 1:

This is a famous proverb in virtually all languages. Best known perhaps from the Roman poet Horace (1st century AD): "Parturient montes, nascetur ridiculus mus" (The mountains will be in labor, and a ridiculous mouse will be brought forth). A common English version is "A mountain gave birth to a mouse".

Solution 2:

full of hot air refers to someone who talks a lot and makes big claims, but with no action behind their words.

Similarly there's all talk no action.

The phrases essentially mean the same thing, the first more emphasises the boastfulness of the subject, the second more emphasises the lack of action.

These terms can be used to refer to anyone - not just people in positions of authority or expected influence.

That politician is full of hot air, he makes all these claims about how he's going to make the world a better place, but really he's all talk and no action.

Solution 3:

"All hat, no cattle" is used in the American West to describe someone who acts like he's a big deal cowboy/cattleman, but is in fact only dressing the part.

Solution 4:

The term damp squib comes to mind.

A situation or event which is much less impressive than expected: my moment of power was a damp squib

_OED

So, in your intended context, you could describe either the under-performing politician or the unimpressive event as a damp squib:

He said he was going to start a revolution but it turned out to be a bit of a damp squib

The Free Dictionary gives a nice note about the origin of this term:

A squib is a type of firework (a small container filled with chemicals which explodes to produce bright lights and loud noises) and if it becomes wet, it will not explode.

The incendiary root dovetails nicely with your idiom's volcano metaphor.