Kosh's arrival on Babylon 5 was a highly anticipated event, but it was marred by an attempt on his life by a rogue faction of the Minbari Warrior Caste. Kosh survived the attack, and went on to serve as the Vorlon ambassador for years.
Kosh's purpose on the station was apparently to rally the Young Races to fight the Shadows when they reawakened. He intended to act only as an advisor, but when John Sheridan insisted on direct military support from the Vorlons to show that the Shadows could be defeated in battle, Kosh ordered the attack. In retaliation, the Shadows assassinated Kosh.
Kosh was succeeded by Ulkesh Naranek.
According to J. Michael Straczynski, "Naranek" is a title, not a name. It's meaning is unknown.