Final answer:
Ares was the least highly regarded of the Olympian gods due to his association with the brutal and bloody aspects of war, compared to other gods who had more esteemed roles.
Step-by-step explanation:
The least highly regarded of the Olympian gods among the Ancient Greeks was Ares (C), the god of war. Unlike Athena, who represented strategic warfare and wisdom, Ares was associated with the brutal and bloody aspects of war. Due to the violent and destructive nature of his domain, as well as his aggressive and tumultuous personality as depicted in mythology, Ares was not as esteemed as other deities such as Poseidon, Athena, or Apollo, all of whom had more complex and constructive roles within the pantheon and human life.