Specifically, it is believed that grey wolves are the ancestors of all domestic dog breeds. Through a process of selective breeding over thousands of years, wolves with certain desirable traits were chosen to reproduce, eventually leading to the wide variety of dog breeds we see today.
While there is no second animal that contributed directly to the creation of dogs, some genetic studies have shown that there may have been a minor contribution from other canid species like coyotes or jackals, but this is still a matter of debate and research.