Word for a person who avoid accountability of his promises by denial and shaming [duplicate]

I'm somewhat vexed in that I cannot think of a word that means a "promise breaker" or "person who breaks a promise". There are words that may subsume that, such as "miscreant" or "liar", but I cannot come up with an English word that is limited to a person who breaks promises.

The closest I've come is "piker", which is (a) informal and (b) limited to Australia/NZ, but means (according to the dictionary on my Mac):

a person who withdraws from a commitment.

Is there a more formal and common word that can be used to refer to people who break promises?

Solution 1:

Reneger:

renege, renegue vb (intr; often foll by on)
to go back (on one's promise, etc.)
reneger , reneguer n

Reneger vs. oath breaker ngram:

Solution 2:

A personal favorite slang term for an unreliable person is a flake. A flake says they are going to do something and then they don't follow through. The definition is not limited to promise breaking, however.