Optimal play in 'Guess Who?'

We prove an optimal strategy for the children’s game Guess Who? assuming the official rules are in use and that both players ask `classical’ questions with a bipartite response. Applying a technique described in [Rabern, B & Rabern, L 2008, ‘A simple solution to the hardest logic puzzle ever’, $\mathit{\text{Analysis}}$, vol. 68, no. 2, pp.~105-112.] allows for questions with tripartite responses; we explain this innovation and give an optimal strategy for two players applying it.