William "Billy" Alexander is the father of Jacqui, Mercedes, Theresa McQueen and Emily Alexander.
Billy attended Kathleen McQueen's fundraiser in February 2011, where Mercedes accused him of touching her. Carmel apologised and accepted Billy's invite of meeting with him for lunch. When Billy went to Carmel's house, he encountered Myra McQueen, who slapped him and revealed that he was Mercedes and Jacqui's father. Billy told his daughters that he was ill and needed a kidney transplant, and they were the only likely donors. They refused, and Kathleen revealed that he was also the father of her daughter, Theresa. Theresa agreed to be a donor and Billy gave her his mother's charm bracelet as a thank you.
Theresa's boyfriend, Ethan Scott, became suspicious of Billy after finding him out drinking with Kathleen. He told Theresa of his suspicions and they followed him as he went to the hospital for kidney dialysis. There, they discovered that Billy was not ill, but his other daughter, Emily, was. Theresa changed her mind about donating, and she also found a text on Kathleen's phone that revealed that she knew of Emily's existence.
Billy supported Jacqui after she reported Gilly Roach for rape, and invited her to stay with them for a while in Spain. Jacqui ended up agreeing to be a donor for Emily but was found to not be a match. Billy and Emily then left, having only been interested in Jacqui for her kidney.