There are multiple origins and meanings for the name:
1. Russian (Иван) & Spanish (Iván) form of the personal name John (Iohannes) - "God is gracious"
2. From Slavic ива [iva] "willow". Willow has had many symbols in in ancient times.
Ivan the Terrible (25 August 1530 - 28 March 1584) was Grand Prince of Moscow from 1533 until his death. His long reign saw the conquest of the Khanates of Kazan, Astrakhan, and Siberia, transforming Russia into a multiethnic and multiconfessional state spanning almost one billion acres, approximately 4,046,856 km2 (1,562,500 sq mi). Ivan managed countless changes in the progression from a medieval state to an empire and emerging regional power, and became the first ruler to be crowned as Tsar of All Russia.