Mr. Fowler is the father of Amy Farrah Fowler.
He was briefly mentioned by Amy in "The Emotion Detection Automation" (S10E14), but no information about him was said.
Because of this, it has been unknown his status of her father is unknown whether he is still married to Amy's mother or divorced.
In "The Proposal Proposal", Amy wants to know if Sheldon asked her dad about the proposal, and Sheldon says he did, "after" asking Stephen Hawking.
He was mentioned again in "The Geology Methodology".