Nikola IV Frankopan (Hungarian: Frangepán Miklós) was the Ban of Croatia and Dalmatia from 1426 to 1432. He was one of the first of his clan to make this name famous in Croatian and Hungarian history. Even before he became Banus, he owned the Island of Krk, the districts of Vinodol, Modruš, Senj, Gacka and Lika in Croatia. His properties also extended to the towns of Cetin, Slunj and Ozalj in Slavonia. When he became Banus, king Sigismund left him in return a loan of 28,000 ducats, also the town of Bihać on Una river, further Knin, Lapacgrad, Vrlika, Ostrovica (near Bribir), Skradin, the county of Luk between Zrmanja and Krka rivers and the district of Poljice. Thus, Nikola Frankopan (Frankapan originally spelled as Frangipani) owned nearly all of Croatia.
In Slavonia the Banal authority belonged to Prince Hermann of Celje (Zell) (1423–1435), Father-in-law of king Sigismund. Hermann was the master of a large part of Slavonia. Because of family quarrels the two powerful clans clashed. Each of them had partisans among the powerful Barons. Thus two factions were formed ready to start a bloody feud. Those who sided with the Princes of Celje (Zell) strove to extend their sway also over Croatia and to annihilate the Frangipani family members as a way to over take their lands, titles and to shift the balance of power towards their favor.
The outbreak of civil war was prevented by Sigismund's return from abroad. Peace was further consolidated by the passing of Banus to Nikola on June 26, 1432. Prince Nikola died in that same year. Some rumors were that he was murdered by opposing Barons loyal to Hermann II of Celje. Some said it was due to another rivalry.
He was survived by nine sons and daughters. The founder of this branch of the Frangipani family supplied great leaders and Generals of Croatian history. Nikola Frankopan was very politically skillful. He arranged special marriages for his children and permanently set his family members in positions to look after the vast amounts of properties that he acquired. Their political opponents used propaganda to create strife for the family. Some of the accusations included that some family members had converted to Islam. The propaganda that spread quickly.
The vast wealth accumulated coupled with the prominent marriage arrangements set the entire family up as easy targets. One family member was beheaded on his way home and couple were suddenly murdered as they were on their way home from church. The culprits were never found, however a cloud of suspicion grew over the family of Hermann II of Celje. This was because of the ongoing tug for political power from King Sigismund who had married Queen Mary of Hungary eldest surviving daughter of Louis I of Hungary 1371– 17 May 1395 but not before plotting an elaborate kidnapping of her and her mother. He then ordered the murder of her mother Queen Elizabeth of Bosnia. He then vindictively ordered the murder of her three cousins Bishop Paul, John, and Ladislaus Horvat. He then murdered Queen Mary of Hungary who was heavily pregnant with his child and in 1406 he remarried Mary's cousin Barbara of Celje the daughter of Hermann II of Celje (Zell).
Elizabeth Frankopan (Frangepan-Frangipani) of Veglia (died 1422) was a relative of Nikola Frankopan. She married Frederick II, Count of Cilli and Ortenburg, Ban of Slavonia, (1454) cousin to Hermann II of Celje (Cilli-Zell) murdered his wife by stabbing her to death when they were spending time together on a reconciliation lover's weekend. He was protected by Barbara and was never punished for his crime. This caused a great internal war because the Frankopan and Anjou Horvat Von Radic de Corbava families were closely related to each other and they had lost two of their most admired female cousins within a short period by the same cluster of families competing for intense superiority.
As a result of the vindictiveness of King Sigismund fueled by the envious gloating of the Celje family members the Frankopan (Frangipani) family altered their surnames and chose to live thereafter in private. This prevented them from further becoming political targets. This proved wise during and after the April 30, 1670, beheadings of Krsto Frankopan and Petar Šubić Zrinski. The surviving family members collectively decided to use the Roman Naming Convention method as a means to somewhat preserve themselves. Some chose to move away from the unrest and live quiet lives. One thing was for certain, the continuous murders and hostile land take overs set in motion a great challenge for this family's survival.
Frankopan also established the monastery which became the center of the town of Crikvenica. He also fortified Omišalj and Krk.