Johann Katzianer (Slovene: Ivan Kacijanar), or Hans Katzianer, Freiherr zu Katzenstein und Fledingen (1491, Begunje (German: Vigaun) – 27 October 1539, Hrvatska Kostajnica) was a Carniolan aristocrat and an Imperial Army commander.
He is first mentioned in 1527 when Ferdinand I, Holy Roman Emperor gathered an army to support his claims on the throne of Hungary, which had become vacant after King Louis II of Hungary was killed in the Battle of Mohács against the Turks.
Katzianer took part in Ferdinand's Hungarian campaign of 1527–1528 against the voivode of Transylvania John Zápolya, who had also been proclaimed King, supported by a large faction of the nobility in the Hungarian kingdom.
Katzianer distinguished himself in the Battle of Tarcal in September 1527 and especially in the Battle of Szina in March 1528, but alienated himself from the population by the violence and misbehaviour of his troops.
After the death of Nicholas, Count of Salm, he was named commander in chief (Obristfeldhauptmann) of the troops in Hungary, where he held off under difficult circumstances new attacks from John Zápolya and Suleiman the Great. He gained a great victory in the Battle of Leobersdorf where he destroyed a Turkish army led by Kasim Bey.
In 1537 he was commander of an army of 24.000 men to besiege Osijek. The campaign was a complete disaster and Katzianer was blamed for fleeing and abandoning his army to be annihilated in the Battle of Đakovo. He was arrested and sent to Vienna to be tried, but escaped before the verdict on 31 January 1538 to Zrinski Castle in Croatia.
Here he contacted enemies of the Habsburgs to plot against Ferdinand, but the young Count Nikola Šubić Zrinski had him murdered, and was stabbed during dinner.