"ISAAC" looks like a military acronym, and if I stop to think about how it's spelled, I'm doomed. I'm not so fond of the name. I do like words that end in "ac" -- Kerouac's name beats the hell out of his writing -- but all things considered, I'm willing to accept Izaak Walton's own bizarre spelling of his name.
He's dead now, anyway. It's too late to argue with the man. Madame Blavatsky isn't returning my phone calls. Maybe she's dead, too . . .
At any rate, the prenominate Izaak Walton lived from 1593 until 1683, anno Domini in both cases. He was an angler, a fisher of trout in the company of John Donne. Why is he remembered? Trout are not an enduring medium. The deeds of anglers are written in water, unless they write 'em on paper themselves. Izaak Walton did just that. In 1653 Izaak wrote The Compleat Angler, or, the Contemplative Man's Recreation, the book he is most remembered for. It's about angling, and about this and that, and some people are annoyed by the way he spelled "complete". It's a bit cutesy, isn't it? Seems so to me, anyhow. It's even got characters with clever allegorical Latin names: "Piscator" is a fisherman, get it? Well, in 1653 people thought that was pretty slick.
Izaak wrote other books also, mostly biographies of his friends: The Life of Sir Henry Wotton, The Life of Mr. George Herbert, The Life of Mr. Richard Hooker, and The Life and Death of Dr. Donne. That last is John Donne, the poet and divine. All four of these guys were poets and/or divines (High Church, naturally) and/or academics of Izaak's acquaintance. Hooker was a bishop. He was a royalist during the English Civil Wars, but he really just cheered from the sidelines.