Little of substance is known about Gordian III. He came to the throne young and died young.
Gordian III was the grandson of Gordianus Africanus and the nephew of Gordian II:
The reverse legend (eternal Rome) of these two coins is somewhat ironic as the two elder Gordians never ruled from Rome.
The elder Gordians became emperors in revolt against Maximinus I.
Maximinus I (Thrax)
The senate apparently hated Maximinus and were quick to recognize the Gordians after his murder. Nevertheless, the regular army had not gone over to the Gordians and the younger Gordian at the head of a Carthaginian rabble was defeated and killed in battle. His father committed suicide at about the same time.
Gordian III was made Caesar under Pupienus and Balbinus to provide a sense of dynastic continuity but also to gain access to the Gordians' vast wealth.
When Pupienus and Balbinus were murdered, Gordian III became emperor in 238 at the age of 13.
RIC 13, LIBERALITAS AVGVSTORVM, Pupienus, Balbinus and Gordian seated on platform
Gordian III married Sabinia Tranquillina in 241. She was the daughter of his praetorian prefect, Timesitheus.
Questions remain about the authenticity of this coin. Certainly the style is right for the period. Most dealers think it is a contemporary (to the period)fake. One dealer thinks it is authentic but burned. Another dealer viewing a processed image of this coin thinks that it is a modern cast fake. Let me know what you think. It was supposedly found recently near a construction site in Belgium.
RIC 250 CONCORDIA AVG, Gordian III and Tranquillina holding hands
This particular coin was offered but not sold in a Triton auction.
Provinicial issues of Tranquillina are much common than imperial. To see some go here.
When Tranquillina's father died in the winter of 243, his deputy Philip the Arab replaced him.
In the east fighting the Persian king Shapur I (239-270), Gordian died under mysterious circumstances in 244. Most scholars expect that Phillip was responsible. Phillip's accession continued the era of military emperors that began with Maximinus I.
Michael Grant calls this period, "the age of crisis."