The plan of the alphabet is derived from the Glagolitic alphabet, a 9th century uncial cursive usually credited to two brothers, Saint Cyril and Saint Methodius.
But the shapes of the glyphs in the Cyrillic alphabet are mainly Greek letters, although some letters retain their Glagolitic forms.
Cyril's contributions to the Glagolitic alphabet and hence to the Cyrillic alphabet are still recognised, as the latter is named after him.