Iapetus, god of mortal life span
Iapetus (Japetus, the Piercer) was a Titan god of mortal life span or god of death. He presided over the timeline of all mortals. His nickname, "the piercer", actually meant that he came for a life of mortals in terms of violence. In other words, when Iapetus decided that one's time had passed, he brought violent death upon him. He was also known as a Pillar of west. Together with his other three brothers Coeus, Hyperion and Crius they presided as the Pillars holding Heaven and Earth apart.
Myths of Iapetus, his family, titanomachy and punishment
The following grouped sections are available:
His family
He was one of six sons of Uranus and Gaea and is mentioned by Apollodorus as one of the five brothers, all but Oceanus, who participated in rebellion against Uranus and later attacked him. When they overcame him, the four brothers probably held him down while Cronus castrated him. During the Golden Age of the Titans, he consorted with an oceanid Clymene, a daughter of Oceanus and Tethys, and fathered Atlas, Menoetius, Prometheus and Epimetheus.
Role of Iapetus in Titanomachy
After decapitating and dethroning their father Uranus, Iapetus stood by his brother Cronus who became a new ruler of the Cosmos. There are a few statements by different authors which indicate that the role of Iapetus was very important and equate him with the role of Cronus. Homer himself states that Cronus and Iapetus were equal in power, while Nonnus and Valerius Flaccus state that during the war, at some point, Zeus fought with Iapetus and according to Valerius Flaccus, who goes even further, it is said that Zeus became the ruler of Cosmos after winning the fierce battle with Iapetus.
It is important to note that Iapetus was also the name of a Giant during Gigantomachy or the war of the giants which is not the same war as the war of the Titans and the Roman authors, such as Valerius Flaccus, likely referred to Iapetus as the giant who Zeus fought in Gigantomachy.
When the war between Titans and Olympian gods had started, his sons were also mentioned to have played their part. Atlas and Menoetius sided with the Titans, while Prometheus and Epimetheus chose Olympians. Atlas became the leader of Titans in the war and caused Olympians more than a few setbacks. His other brother Menoetius was said to be very vicious, brutally slaying allies of Olympians until Zeus himself struck him down with a thunderbolt and sent him to Tartarus because of his mad presumption and exceeding pride.
Prometheus and Epimetheus, although they had also played an important part in the war, were also, like their father, very rarely mentioned during the war. Instead they played an important role after the war, with creation of men and animals.
Released from prison
When the war was over, Iapetus was sent to Tartarus where he was re-united with his brothers and many relatives. He was described by Homer as one of the more destructive titans who was seated beside Cronus in the depths of Tartarus. However, according to Aeschylus' lost play, he was later released by Zeus from Tartarus with the rest of the titans.
Sources
To learn more, you may explore the sources and notes about Iapetus yourself