He was a famous Arabic mathematician, a pioneer of algebra and algorithms (both named after him).

(Just kidding. I also didn't know the answer, not having read SICP, this would be my guess, but I believe axblount is right.)

Author lists often end with "et al" which is Latin for "and others."

I'm going to name my kid "al Arthur Alexander", so he can claim authorship credit for thousands of writings, and also for millions of highscores in arcade cabinets everywhere.