Usually addressed as Hilda , she is a demon maid who helps Oga take care of Beelzebub IV.
She reveres the Demon Lord and feels that it is a great honour to be chosen as the child's "Mother" or caretaker. Her most characteristic features include her Gothic Lolita appearance and frontal assets. She owns an umbrella which conceals a sword in the handle.

She takes being Beel's mother quite seriously and even goes as far as to state that it was the only reason for her existence. As a fighter she is quite skilled. Her skills gained her the nickname "Oga's Bride" at Ishiyama. Hilda and Oga's rapport is pragmatic for the most part. Hilda often looks down on him and never hesitates to mock him but at the same time acknowledges his strength and allies with him in Beel's interest.

In the anime she has developed an interest in watching soap opera, much to Oga's disbelief.
Her name comes from the Old High German name "Hildegard", meaning Hild (war or battle) and Gard (protection) and means "protecting battle-maid".

Source:Wikipedia