Final answer:
Lev Davidovich Bronstein, better known as Leon Trotsky, took the nickname 'Trotskii' from one of his jailers in Odessa. The question refers to a historical moment likely related to Trotsky's use of aliases during his revolutionary activities.
Step-by-step explanation:
The person Lev meets on the road is not explicitly mentioned in the provided reference from Montefiore's Young Stalin. However, according to historical accounts, Lev Davidovich Bronstein is better known as Leon Trotsky, a prominent figure in the Russian Revolution. The nickname 'Trotskii' was taken from one of his jailers in Odessa and subsequently used while traveling on a forged passport.
This transformation into 'Trotsky' became part of his revolutionary identity. The dialogue, "Who are you?" asked I, suggests an encounter with an unfamiliar person, perhaps reflecting a moment when Trotsky was using one of his aliases and interacting with someone unaware of his true identity.