Petru Rareș (pronounced [ˈpetru ˈrareʃ]), sometimes known as Peter IV (Petru IV; ca. 1487 – 3 September 1546) was twice voievod of Moldavia: 20 January 1527 to 18 September 1538 and 19 February 1541 to 3 September 1546. He was an illegitimate child born (probably at Hârlău) to Ștefan cel Mare. His mother was Maria Răreșoaia of Hârlău, whose existence is not historically documented but who is said to have been the wife of a wealthy boyar fish-merchant nicknamed Rareș "rare-haired" (i.e., bald). Rareș thus was not Petru’s actual name but a nickname of his mother’s husband.
In his youth he was a fish merchant, but Prince Ștefăniță, grandson of Ștefan cel Mare, on his deathbed, recommended Petru as a suitable contender to the throne, thus acknowledging Petru's blood lineage from Ștefan cel Mare.
Petru exhibited many of his father's qualities: ambition, daring, bravery, piety, artistic taste. However, he was marked by inconstancy and a lack of political instincts.
In the Hungarian battles between Ferdinand Habsburg and John Zápolya, he initially sided with Ferdinand, but when the Ottomans awarded recognition to Zápolya, he switched allegiances. In exchange for the citadel of Bistrița, he entered Transylvania on Zápolya's side and crushed Ferdinand at Feldioara on 22 June 1529. Zápolya then gave him Ungurașul but in spite of the efforts made Rareș was unable to occupy Bistrița. Neither could he subdue Brașov, which he besieged again in October for several weeks. Thus he was far from realizing his plan of ruling Transylvania. He had to content himself with Ciceu and Cetatea de Baltă, ruled by his father, and with the bishopric of Vad.