Juan Núñez I de Lara y León (died Córdoba, April 1294), also known as "el Gordo" or "the Fat", was a Spanish noble.

He was the head of the House of Lara, Lord of Lerma, Amaya, Dueñas, Palenzuela, Tordehumos, Torrelobatón, and la Mota.

[2] Juan Núñez I de Lara accompanied King Louis IX of France and Theobald II of Navarre during the Eighth Crusade and was with them in Tunis.

During the revolts of the nobility of 1272–1273, in which Juan Núñez I supported the positions of his father and other rebel magnates against the infante Philip of Castile.

Juan Núñez tried to remain loyal to the king, who had at the beginning of the rebellion, given him a mission together with Gonzalo Pérez Gudiel, the bishop of Cuenca, to persuade the infante Philip and other magnates to break their agreements with the Kingdom of Navarre.

Following this unsuccessful attempt, Juan Núñez accompanied his father, Nuño González de Lara "el Bueno" when he and the rebellious magnates abandoned the Kingdom of Castile and Leon and sought refuge in the Nazarí Emirate of Granada.

At the beginning of 1273, Juan Núñez I de Lara, who had up until now acted as a mediating force together with the bishop of Cuenca between his father and the King, abandoned the Castilian crown and embraced his role as a rebellious noble.

Despite the betrayal of many of his nobles, it was Alfonso's wish to pursue his goal of attaining the Fecha del Imperio (title of the Holy Roman Emperor).

After much negotiation, Alfonso X, advised by his brother Frederick of Castile and Simón Ruiz de los Cameros, the Castilian monarch accepted most of the demands of the exiled nobles, presenting the final agreement to Nuño González de Lara "el Bueno", who in 1273, met with the queen, Violant of Aragon in the city of Córdoba.

It was not until early the following year, 1274, when Nuño González de Lara "el Bueno" and his children, amongst other nobles, were allowed back onto the rolls themselves.

[4] Juan Núñez' father, Nuño González reappeared on the royal rolls on 24 January 1247 and was reinstated to privileges not received since 14 July 1272.

During the absence of Alfonso X of Castile, Juan Núñez I accompanied the infante Ferdinand de la Cerda as he carried out his official duties.

On 25 July 1275, the infante Ferdinand de la Cerda died in Ciudad Real whilst awaiting reinforcements in a fight against the Marinid Dynasty in Andalucía.

Lope Díaz III agreed to help Sancho obtain his claim to the throne of Castile and supplant the Cerda infantes in return for protection of his interests.

Lope Díaz III gathered his vassals at Ciudad Real to announce his decision to support Sancho's claim to the throne as Alfonso X's legitimate successor.

After Alfonso X and Peter III of Aragon came to an agreement at Vistas de Campillo that the Aragonese monarch would renounce his rights over the Señorío de Albarracín, the infante Sancho IV, who had become an enemy of his father on the issue of the Cerda infantes, solicited the Aragonese monarch to support his claims to the Castilian throne in return for his reinstatement to lordship over Albarracin.

In 1289, after coming to an agreement with Sancho IV over the towns of Moya and Cañete, Juan Núñez I returned to the Kingdom of Castile and sent his daughter, Juana Núñez de Lara to María de Molina, wife of Sancho IV so that she could be raised in the court as agreed by the agreement aforementioned.

Juan Núñez I continued his war against the Kingdom of Aragon and against Diego Lopez IV de Haro who died in 1289.

In April 1290, Juan Núñez I was with the king at Burgos when some members of the court alienated the lord of Lara by telling him that Sancho IV was plotting his death.

Shortly after moving to the Kingdom of Aragon, Juan Núñez I began to dedicate himself to the recuperation of the señorío de Albarracín.

Juan Núñez I vowed to aid Alfonso III of Aragon in his fight against Sancho IV and to give refuge in his castles to the Aragonese monarch and his troops.

By the end of 1290, Juan Núñez I had become angry with the King of Aragon for although he had been promised the return of lordship over Albarracín, it became evident that this deal would never happen.

The king's brother fled to the Kingdom of Portugal and Juan Núñez II was obliged to seek reconciliation with Sancho IV.

Further, after he was set free by the infante John, Juan Núñez I solicited the protection of King Denis of Portugal, who helped him return to the Kingdom of Castile.

Shortly after, Sancho IV of Castile sent Juan Núñez I to Andalucía to defend the frontier against the armies of Muhammed II al-Faqih who had allied himself with the King of Morocco.