Peter (Hungarian: Velencei Péter; 1010 or 1011 – 1046, or late 1050s), known as Peter Orseolo or Peter the Venetian, was King of Hungary twice. He first succeeded his uncle, King Stephen I, in 1038. His favoritism towards his foreign courtiers caused an uprising which ended with his 1041 deposition. Peter was restored in 1044 by Henry III, Holy Roman Emperor. He accepted the Emperor's suzerainty during his second reign, which ended in 1046 after a pagan uprising. Hungarian chronicles are unanimous that Peter was executed by order of his successor, Andrew I, but the chronicler Cosmas of Prague's reference to his alleged marriage around 1055 suggests that he may also have survived his second deposition.

Peter Orseolo was born in Venice, the only son of Doge Otto Orseolo. His mother Grimelda was a sister of Stephen I, the first King of Hungary; historian Gyula Kristó suggests that he was born in 1010 or 1011. The Venetians rose up and deposed Otto Orseolo in 1026. Peter did not follow his father, who fled to the Byzantine court in Constantinople; he instead went to Hungary, where his uncle appointed him commander of the royal army.

Emeric, Stephen's only son to survive infancy, died in an accident in 1031. Stephen's cousin Vazul had the strongest claim to the throne, but the King overlooked him and named Peter as his heir. On Stephen's order, Vazul was blinded shortly thereafter and his three sons – Levente, Andrew and Béla – exiled, which strengthened Peter's right of succession. The King asked Peter to take an oath respecting the property of his wife, Queen Giselle, suggesting that Peter's relationship with his aunt was tense.

Peter succeeded King Stephen I, who died on 15 August 1038, and adopted an active foreign policy. Hungarian troops plundered Bavaria in 1039 and 1040, and invaded Bohemia in 1040 to assist Duke Bretislav I against Holy Roman Emperor Henry III. Hungarian chronicles recount that Peter preferred the company of Germans ("who roared like wild beasts") and Italians ("who chattered and twittered like swallows"), which made him unpopular among his subjects. He introduced new taxes, seized Church revenue and deposed two bishops.

Audaciously, Peter confiscated Queen Giselle's property and took her into custody. She sought help from Hungarian lords, who blamed one of Peter's favorites (Budo) for the monarch's misdeeds and demanded that Budo be put on trial. When the King refused, the lords seized and murdered his unpopular advisor and deposed the monarch in 1041. They elected a new king, Samuel Aba, who was a brother-in-law or another nephew of King Stephen I.

As soon as he began to rule, Peter threw aside every trace of the forbearance befitting a monarch's majesty, and in consort with Germans and Latins raged with Teutonic fury, treating the nobles of the kingdom with contempt and devouring the wealth of the land "with a proud eye and an insatiable heart." Fortifications, castles, and every office in the kingdom was taken away from the Hungarians and given to Germans or Latins. In addition, Peter was extremely debauched, and his hangers-on behaved with shameful and unbridled lust, violently assaulting the wives and daughters of the Hungarians wherever the king travelled. No one at the time could feel sure of the chastity of his wife or daughter in the face of the importunity of Peter's courtiers.

— Simon of Kéza: The Deeds of the Hungarians

Peter first fled to Austria, seeking the protection of his brother-in-law, Margrave Adalbert. He approached Emperor Henry III for help against Samuel Aba. The new Hungarian monarch invaded Austria in February 1042, but Adalbert routed Aba's troops. Henry III launched his first expedition against Hungary in early 1042. His forces advanced north of the Danube to the river Garam (Hron, Slovakia). The Emperor planned to restore Peter, but the locals were strongly opposed. Accordingly, the Emperor appointed another (unnamed) member of the Hungarian royal family to administer the territories.