Possible Clues:

• Mar. parade celeb
• He rid Ire. of snakes, as the legend goes
• Annual winter honoree, briefly
• Hist. figure with a holiday named after him
• Mar. 17 figure, from 58-Across
• Patron of puking outside Irish pubs before noon, casually
• Mar. 17 man
• Green land patron, for short
• March VIP, briefly
• Patron figure of getting hammered at 9:00 a.m., for short