Solomon was Davids son. After hearing about Solomon's friendship with demons he was supposed to kill, David disowned him.
Tamar was Solomon's sister. The two had a normal sibling relationship, even after Solomon was disowned. Even though Tamar loved Solomon, she still hated the fact that he would not destroy demons, despite having the power to do so.
Dantalion was the first demon to be summoned by Solomon, and although Dantalion had hatred for Solomon in the beginning, he soon becomes close to him. As Solomon's familiar, Dantalion was required to do whatever Solomon wanted. When Solomon ordered Dantalion to kill him, Dantalion was forced to and was deeply saddened to have killed him.
After Sitri was cast out of heaven, he sought refuge with Solomon in his castle. Sitri then flew into a rage when it was revealed that Dantalion was the one who murdered Solomon, not knowing that it was requested by Solomon himself.
Solomon and William have a very complicated relationship. They both have respect for each other,though not much. William calls Solomon an Old Senile fool. And Solomon seems to find William amusing,but possibly annoying,and calls him stuck up.
Camio has respect for Solomon, and he was also saddend when Solomon died.