St John of the Ladder, also known as St John Climacus, was a seventh century monk and abbot of St. Catherine’s monastery at Sinai. His feast days are 30 March and he is also remembered especially on the fourth Sunday of Great Lent.
He lived in the monastery from the age of about 16 until his death in 649. His most famous book is The Ladder of Divine Ascent, after which he is now known. This book is one of the most widely read among the Orthodox, especially during Great Lent.
For more information: orthodoxwiki.org/John_Climacus