Béla the Blind (Hungarian: Vak Béla; Croatian: Bela Slijepi; Slovak: Belo Slepý; c. 1109 – 13 February 1141) was King of Hungary and Croatia from 1131 to 1141. He was blinded along with his rebellious father Álmos on the order of Álmos's brother, King Coloman of Hungary. Béla grew up in monasteries during the reign of Coloman's son Stephen II. The childless king arranged Béla's marriage with Helena of Rascia, who would become her husband's co-ruler throughout his reign.

Béla was crowned king at least two months after the death of Stephen II, implying that his accession to the throne did not happen without opposition. Two violent purges were carried out among the partisans of his predecessors to strengthen Béla's rule. King Coloman's alleged son Boris tried to dethrone Béla but the king and his allies defeated the pretender's troops in 1132. In the second half of Béla's reign, Hungary adopted an active foreign policy. Bosnia and Split seem to have accepted Béla's suzerainty around 1136.

Béla was the only son of Duke Álmos—the younger brother of King Coloman of Hungary—by his wife, Predslava of Kiev. Historians Gyula Kristó and Ferenc Makk write that Béla was born between 1108 and 1110. Álmos devised several plots to dethrone his brother. In retaliation, the king deprived Álmos of his ducatus or "duchy" between 1105 and 1108. Álmos did not give up his ambitions and King Coloman had him and the child Béla blinded between 1112 and 1115 to secure a peaceful succession for his own son, Stephen. According to one of the two versions of these events recorded in the Illuminated Chronicle, the king even ordered that Béla should be castrated but the soldier who was charged with this task refused to execute the order.

[The] King took the Duke and his infant son Bela and blinded them. He also gave orders that the infant Bela should be castrated. But the man who was instructed to blind them feared God and the sterility of the royal line, and therefore he castrated a dog and brought its testicles to the King.

— The Hungarian Illuminated Chronicle

After their blinding, Álmos lived in the monastery of Dömös, which he had founded. Kristó and Makk write that it is probable that Béla lived with his father in the monastery. The Annales Posonienses relates that "the child was growing in the reign of King Coloman's son, Stephen", who ascended the throne in 1116. Having hatched a failed plot against the king, Álmos left the monastery and fled to Constantinople in about 1125. For unknown reasons, Béla did not follow his father to the Byzantine Empire. The Illuminated Chronicle narrates that he was kept "concealed in Hungary from the fury" of the king. Béla settled in the Pécsvárad Abbey, whose abbot sheltered him in secret.

Álmos died in exile on 1 September 1127. According to the Illuminated Chronicle, Béla's partisans "revealed to the King, who believed him to have died after his blinding, that Béla was alive". On hearing this, King Stephen II "rejoiced with great joy, for he knew beyond doubt that he would have no heir". The king even arranged Béla's marriage with Helena of Serbia and granted Tolna to the couple around 1129.

King Stephen II died in early 1131. A late source—the Ottoman Turkish chronicle known as Tarih-i Üngürüs or The History of the Hungarians—narrates that Béla ascended the throne after his predecessor's nephew Saul, whom Stephen II had nominated as his heir, had died. Béla II was crowned in Székesfehérvár on 28 April, substantiating the reliability of this report. However, no scholarly consensus on the exact circumstances of Béla's ascension exists. According to Gyula Kristó, Béla was crowned by Archbishop Felician after a civil war between his and Saul's partisans, but Pál Engel does not mention any conflict related to Béla's succession.