Croatian anti-Ottoman warrior, captain of Senj and lord of Klis fortress (?, around 1490 - Solin, 12 March 1537). Around 1513 he performed military service in Klis, the captain of which he became before 1520. In addition to military authority in the Klis fortress, he also received the civil authority of the count in the suburbs. In 1522, along with Grgur Orlovčić, he was appointed captain of Senj, and since then he has been called "captain of Senj and lord of Klis". He defeated the Ottomans near Klis (1524) and Senj (1525) and brought aid to besieged Jajce.
Accepting the policy of king Ferdinand I, he hoped for more royale help and more regular payment for his brave soldiers. Only the Lupoglav estate in Istria was confirmed to him in the name of the costs of maintaining the fortifications. As he did not receive the necessary help from the king, in 1529 he resigned as the captain of Senj and devoted himself to the defense and supply of Klis, which, as the southernmost Croatian fortress, remained separated from the rest of Croatia due to the Ottoman and Venetian conquests.
During the same period, he often stayed in Lupoglav, and after numerous requests, he received permission to keep ships on a standby in nearby Lovran, his main headquarters, if needed to supply Klis. He thus laid the foundations for the Uskok navy. In 1532, he captured and destroyed the Ottoman fortress in Solin, which blocked the supply of Klis by sea.
When the Ottomans besieged Klis at the end of 1536, he brought military aid which landed in the port of Solin. They soon had to retreat before the new Ottoman forces arrived which invaded Solinsko polje. He was killed while retreating, while trying to board a ship that could not sail out due to the shallow waters. The Ottomans recognized him, arrested him and killed him. Most of his Uskoks took refuge in Senj. The fall of Klis and his death resonated in Croatia at the time as an extremely tragic event, which lost southern Croatia for a long period of time. In Croatian historiography, Captain Petar Kružić is considered as one of the most famous and well-respected Croatian warriors in the period of anti-Ottoman wars.