My offhand comment about Barack Obama having been a "professor" at the University of Chicago triggered some surprising feedback: Was Obama really a professor, the questions run, or was he just an instructor or some kind of lecturer? I had thought this question was resolved a long time ago, but I guess not. Anyway, the University of Chicago Law School put out the following press release on the question a while back:

From 1992 until his election to the U.S. Senate in 2004, Barack Obama served as a professor in the Law School. He was a Lecturer from 1992 to 1996. He was a Senior Lecturer from 1996 to 2004, during which time he taught three courses per year. Senior Lecturers are considered to be members of the Law School faculty and are regarded as professors, although not full-time or tenure-track. The title of Senior Lecturer is distinct from the title of Lecturer, which signifies adjunct status. Like Obama, each of the Law School's Senior Lecturers has high-demand careers in politics or public service, which prevent full-time teaching. Several times during his 12 years as a professor in the Law School, Obama was invited to join the faculty in a full-time tenure-track position, but he declined.

So the school says he was a professor; he was carrying a full teaching load; he was teaching serious courses like con law; and (if I recall correctly from my time visiting at Chicago) he had a permanent faculty office in the law school. Labels are funny things in academia, as Tim Wu has discussed. But to my mind, Obama was a professor.