That would be the Reverend Ralph Abernathy, who later turned from the left to become much more reasonable. And yes, the details of what MLK did at the Lorraine motel the night before he was killed are rather salacious. MLK was no saint.
Was that where some folks got a quote (can’t quote it on a family-friendly website) where Mike King (some say his real name, never changed) made some rather crazy statements about his indiscretions?