Who is the monster of the gray rock Odysseus refers to?

In Homer's "Odyssey," the "monster of the gray rock" refers to Scylla, a sea monster that resides in a cave on a rocky cliff. Odysseus encounters Scylla while navigating the strait between her and Charybdis, another perilous sea creature. Scylla is known for her ferocity and the way she snatches sailors from passing ships, making her one of the many dangers Odysseus faces on his journey home.