Mr. Ollivander knew.
Mr Ollivander touched the lightning scar on Harry's forehead with a long, white finger.
"I'm sorry to say I sold the wand that did it," he said softly. "Thirteen and a half inches. Yew. Powerful wand, very powerful, and in the wrong hands ... Well, if I’d known what that wand was going out into the world to do ..."
He shook his head and then, to Harry's relief, spotted Hagrid.
Harry Potter and the Philosopher's Stone, by way of Pottermore
He obviously knew who Voldemort was, because he knew that Voldemort gave the scar, and he knew Voldemort's wand, and he knew that he sold that wand to Tom Riddle.
