Owner(Mama) is the lovely owner of the Akeno Pub, but that is not her name, nor is she Masa-san's mother. The title of ママ (Mama) is a general term used for the proprietress of a bar.
She is a stunning and quiet beauty. Her dark hair is pulled into a bun and always wearing a yukata behind the bar. Normally, she is only shown to be tending to the dishes as Masa-san talks.
She appears in the omake special feature called "Today's Masa-san". This is shown at the end of the anime "My Bride is a Mermaid! (seto no hanayome)". In this special scene Masa-san talks to a certain someone and offers life advice. He will request Mama to prepare that person a drink. Who he is speaking to is normally not revealed until the very end and has a comedic event.