Today belongs to the letter I. Thus, our saint is Saint Isidore of Seville:
Saint Isidore of Seville (Latin: Isidorus Hispalensis; c. 560 – 4 April 636) served as Archbishop of Seville for more than three decades and is considered, as the 19th-century historian Montalembert put it in an oft-quoted phrase, “The last scholar of the ancient world”.
At a time of disintegration of classical culture, and aristocratic violence and illiteracy, he was involved in the conversion of the royal Visigothic Arians to Catholicism, both assisting his brother Leander of Seville, and continuing after his brother’s death. He was influential in the inner circle of Sisebut, Visigothic king of Hispania. Like Leander, he played a prominent role in the Councils of Toledo and Seville. The Visigothic legislation that resulted from these councils influenced the beginnings of representative government.
His fame after his death was based on his Etymologiae, an etymological encyclopedia which assembled extracts of many books from classical antiquity that would have otherwise been lost.
Much more can be learned about this influential saint at his wiki, located here.