Bill Horton, born in 1940, was the fourth youngest of the Horton children. Bill's siblings include twins Tommy Jr. and Addie as well as Mickey and Marie. Bill started the show as a recent Harvard graduate and aspiring surgeon.

It was at the hospital where he first met and began dating Laura Spencer. When his brother Mickey also became interested in Laura the two brothers clashed over her. Eventually Laura and Bill became engaged and the two planned to marry, but when Bill was stricken with bone tuberculosis in his hand it seemed likely Bill would never be a surgeon. Devastated Bill left Salem to sort out his future and eventually took a medical position in another town.

In late 1967, Bill returned to Salem along with his friend Dr. Mark Brooks and a little boy name Timmy McCall. Bill had been living with the McCall family when Timmy's mother Mary died, but before passing made Bill promise to become Timmy's guardian. He met Mark Brooks through Mary, and it was Mark who encouraged Bill to undergo therapy to regain control of his hand. When Timmy McCall needed his appendix removed Bill performed the surgery, and knew he would be able to return to Salem and continue his surgical career.

After Mickey and Laura had wed, Bill was consumed with jealousy. One night while drunk Bill raped Laura in her office. When he came to the next morning Bill could not remember everything that had happened, and Laura told him she had turned him away, in order to prevent any feuds among her husband and Bill.

In 1968 Bill would discover that he was the father of the child Laura was carrying when he accidentally saw the results of Mickey's sterility test in Tom's office. Bill kept the knowledge a secret, and after the baby was born Bill decided it would be best that nobody knew Bill knew the truth about the baby. Bill let his brother Mickey continue to believe he was the father of Michael Horton.

Everyone's happiness would soon be ruined when Bill learned that Kitty Horton had a tape recording of Laura and Tom Horton talking about Michael where they revealed he was Michael's natural father. Bill went to Kitty's apartment and refused to play games. Bill ransacked her apartment and fought with Kitty before finding the tape and leaving. That wasn't the last troubles Kitty would cause for the Horton family. Bill would eventually be charged with Kitty's murder and Mickey would defend Bill in court. Bill refused to tell anyone why he was at Kitty's place that night, and eventually he would be found guilty of involuntary manslaughter and be sentenced to 3 years in jail.

In jail Bill would meet Doug Williams, and his stories of Salem and a rich widowed Susan Martin would send Doug to Salem after he was released. Near the end of 1970 Bill was released from prison and later began seeing his brother's secretary Linda Patterson.

In 1972 Bill and Laura began to fall in love when Laura learned the true reason Bill went to jail. Laura planned to divorce Mickey and marry Bill. When the two were overheard talking by Mike, Mike assumed they were having an affair and ran out into the street and was hit by a car. Mike would survive, but afterward he told his uncle Bill he hated him and to stay away from his family.

In 1973 Mickey would suffer a massive coronary, but with Bill's skilled hands he managed to save his brothers life. Soon after his operation Mickey would suddenly disappear from Salem. With Mickey out of the way Bill was free to pursue Laura, but her marriage to Mickey still stood in the way. When Mickey was discovered to be alive he granted Laura a divorce so he could remain with Maggie Simmons.

On December 4, 1975 Bill and Laura Horton were married, and a year later Laura gave birth to their daughter Jennifer Rose Horton on September 11, 1976.

In 1976 the truth about Mike's parentage came out when Mike was injured while repairing a truck on Maggie Simmons' farm. Mickey and Laura both donated blood to save Mike's life, but neither matched. Mickey found out through Bill's medical records that Bill was a match, and Mickey's memory quickly flooded back. Mickey was enraged and bought a gun and went after Bill. Mickey waited for Bill to come home, and when he did they both fought over the gun. Bill ended up being shot in the arm, and Mickey suffered a mental breakdown. Mickey would be admitted to Belview Sanitarium for one year following the incident.

After the birth of his daughter Jennifer, Bill's wife Laura fell into a deep depression, but overcame it with the help of Bill and Dr. Marlena Evans.

In 1977/78 Bill began an affair with a coworker Dr. Kate Winograd. He eventually left Laura to live with Kate, but when he realized he still loved Laura he returned to her and tried to repair their relationship.

In 1980, after putting his wife Laura into a sanitarium, Bill left Salem and left his daughter Jennifer with Tom and Alice Horton.

Bill returned in 1987 and began dating Janice Barnes. He eventually broke things off when his guilt about Laura grew too strong. Bill then focused his attention on Jennifer and tried to put an end to his daughter's relationship to Frankie Brady. She retaliated by becoming engaged to Frankie, but broke it off when she feared she may become schizophrenic like her mother and grandmother.

Bill would leave Salem in 1988, but visit again in 1991 and 1992. He also briefly returned in 1994 when Laura came home from the sanitarium after being catatonic for nearly 17 years. He also wanted to meet his son, Lucas, whom he had just discovered was the product of an affair he had with Kate Roberts many years before. Unfortunately, Bill was coldly greeted by the young man. After that, Bill went back to Africa, but, years later, Lucas would visit him and the two would make amends.

In the winter of 2010, Bill returned to Salem for Mickey's funeral, although the character was never seen on-screen. Sadly, Bill would visit Salem once again in June 2010 when his mother's health began to decline. Along with Laura, he showed up at the Horton House where Jennifer welcomed her parents.

Later, Bill greeted Kate when she stopped by with flowers for Alice. Laura was furious that Kate was there, but Bill tried to maintain the peace between them. However, when Kate asked, he did note that he and Laura had not reunited Đ they had met at the airport and drove together to Alice's house.

Bill remained at his mother's side as she continued to slip away. During that time, he also caught him with his family and joined in baking Alice's famous doughnuts. Sadly, Alice passed away on June 23, 2010. The loss of his mother devastated Bill, but he remained strong for his family.