Pope-elect Stephen
Pope-elect Stephen II was a Roman priest elected pope in March 752 to succeed Zachary; he died of a stroke a few days later, before being ordained a bishop. In 745, Zachary had made him a cardinal presbyter, with the titulus of San Crisogono, the same titulus later held by Cardinal Frederick of Lorraine, who became Pope Stephen IX.
The Annuario Pontificio attaches to its mention of Stephen II (III) the footnote: "On the death of Zachary the Roman priest Stephen was elected; but, since he died three days later and before his consecratio, which according to the canon law of the time was the true commencement of his pontificate, his name is not registered in the Liber Pontificalis nor in other lists of the popes."
From 752 to 942, eight who bore the name Stephen, including this priest, were elected pope, but only seven reigned as pope. Regnal numbering was not used for popes until the 10th century, and any numbering attached to them has been applied posthumously. The first pope to take the name Stephen after numbering became customary was called Stephen IX during his lifetime and signed all his documents "Stephanus Papa Nonus".