Many poets have been acquainted with the night; some have been intimate with it; and a handful have been so haunted and intoxicated by the darker side of existence that it can be hard to pick them out from the murk that surrounds them. As Poems 1959-2009 (Farrar, Straus & Giroux, $40) demonstrates, Frederick Seidel has spent the last half-century being that darkest and strangest sort of poet. He is, it’s widely agreed, one of poetry’s few truly scary characters. This is a reputation of which he’s plainly aware and by which he’s obviously amused, at least to judge from the nervy title of his 2006 book, Ooga-Booga. This perception also colors the praise his collections typically receive — to pick one example from many, Calvin Bedient admiringly describes him as “the most frightening American poet ever,” which is a bit like calling someone “history’s most bloodthirsty clockmaker.” What is it about Seidel that bothers and excites everyone so much?