I answered the titular question on Quora as follows:
“‘A corporation is a legal person just as much as an individual,’ said the Court in Sheffield, etc., Bldg. Society, 22 Q. B. D. 476. And in Society v. Abbott, 2 Beav. 567, Lord Langdale, M. R., held that, as in this case, great confusion arises by failure to distinguish the body corporate from the individuals who constitute, ‘not the corporation, but all the members of the corporation.’” Jackson v. Hooper, 75 A. 568, 571 (N.J. 1910).
“What is a legal person is for the law, including, of course, the Constitution, to say, which simply means that upon according legal personality to a thing the law affords it the rights and privileges of a legal person ….” Byrn v. New York City Health & Hosps. Corp., 286 N.E.2d 887, 889 (N.Y. 1972).
“To speak of a corporation as ‘a legal person’ is a convenient figure of speech used to describe the corporation as a legal unit, a separate concern with a capacity, like a person's, to hold property and make contracts, to sue and be sued, and to continue to exist notwithstanding changes of its shareholders or members.” ECR Properties, LLC v. Camden County Dev., LLC, 998 F. Supp. 2d 1295, 1311 (M.D. Ala. 2014).