Captain James Tiberius Kirk is considered one of the most important captains of the Enterprise and commands not only the Enterprise NCC-1701, but also the follow-on model NCC-1701-A. His service aboard the Enterprise eventually earns Kirk the rank of admiral. However, he loses this rank after "Star Trek III" because he acts on his own against Starfleet rules. He eventually becomes captain again and takes command of the Enterprise NCC-1701-A in "Star Trek V: At the Edge of the Universe" and "Star Trek VI: The Undiscovered Country".