Short answers, pulled from the story.
Christian IV reigned for 59 years and 330 days, making him the longest-reigning monarch in Scandinavian history by duration of holding the title. He became king on the 4th of April 1588 at age ten and died on the 28th of February 1648.
After a devastating fire in August 1624 destroyed much of Oslo, Christian IV decided the old city should not be rebuilt on its original site. He ordered it relocated to the area below Akershus Fortress and renamed it Christiania after himself. The name remained in use until 1925, when the city reverted to Oslo.
On the 1st of July 1644, while commanding his fleet aboard the Trinity, a Swedish cannonball exploded a nearby cannon and sent splinters of wood and metal into Christian's body, wounding him in thirteen places and blinding one eye. He was knocked to the deck but rose immediately, called out that he was unharmed, and remained on deck until the battle ended.
Christian IV founded numerous cities, including Christianopel in 1599, Christianstad in 1614, Glückstadt in 1617, Christianshavn in 1619, Kongsberg in 1624, Christiania (now Oslo) in 1624, and Kristiansand in 1641. He is considered the Nordic head of state credited with founding the highest number of new cities in his realm.
Denmark's first colony in India was established at Tranquebar (now Tarangamabadi) on India's south coast by a treaty signed on the 20th of November 1620. Admiral Ove Gjedde led the expedition, appointed by Christian IV in 1618, which took two years to reach its destination and lost more than half its crew. The Nayak of Tanjore negotiated the treaty granting the Danes the village and the right to build Fort Dansborg.
Christian IV entered the Thirty Years' War on the 9th of May 1625 and was decisively defeated at the Battle of Lutter on the 27th of August 1626. He concluded the Treaty of Lübeck in May 1629 without losing territory but was barred from further involvement in the war. The subsequent Torstenson War ended with the Treaty of Brömsebro on the 8th of February 1645, which forced Denmark to cede Gotland, Ösel, and Halland and gave Sweden supremacy of the Baltic Sea.