Herb Simon, polymath.
Here’s the solution to last month’s puzzle. You’re noticing the empty cells, right? They all represent the same letter, but since that letter didn’t appear in the puzzle grid, you could fill in any letter not already used. But to solve the second part of the puzzle, you need to pick the right letter. It turns out that if you fill in those empty slots with the letter M, you can rearrange the nine letters to spell HERBSIMON, i.e., Herb Simon, or as Wikipedia puts it, “one of the most influential social scientists of the 20th century.”