The phrase "number 1" can be replaced by a myriad of synonyms, each carrying slightly different connotations. For example, "top dog" signifies a dominant figure, while "champion" implies success in a competition. "Leader" and "pioneer" suggest someone who is at the forefront of their field, while "kingpin" and "heavyweight" have more of a criminal undertone. Other options include "prime," "foremost," "premier," "front-runner," "best," and "supreme." Ultimately, the choice of synonym depends on the context and the specific meaning that needs to be conveyed.