quality:corruption, linguistic:voice_change
First emigration and second marriage (1902–1903)

Until this point, Trotsky had used his birth name: Lev (Leon) Bronstein. He changed his surname to "Trotsky", the name he would use for the rest of his life. It is said he adopted the name of a jailer of the Odessa prison in which he had earlier been held. This became his primary revolutionary pseudonym. After escape from Siberia, Trotsky moved to London, joining Georgi Plekhanov, Vladimir Lenin, Julius Martov, and other editors of Iskra. Under the pen name Pero ("quill" or "pen"), Trotsky soon became one of the paper's leading writers.

Unknown to Trotsky, the six editors of Iskra were evenly split between the "old guard" led by Plekhanov and the "new guard" led by Lenin and Martov. Plekhanov's supporters were older, and had spent the previous 20 years together in exile in Europe. Members of the new guard were in their early 30s and only recently emigrated from Russia. Lenin, who was trying to establish a permanent majority against Plekhanov within Iskra, expected Trotsky, then 23, to side with the new guard. In March 1903 Lenin wrote:

I suggest to all the members of the editorial board that they co-opt 'Pero' as a member of the board on the same basis as other members. We very much need a seventh member, both as a convenience in voting (six being an even number) and as an addition to our forces. 'Pero' has been contributing to every issue for several months now; he works, in general, most energetically for the Iskra; he gives lectures (in which he has been very successful). In the section of articles and notes on the events of the day, he will not only be very useful, but absolutely necessary. Unquestionably a man of rare abilities, he has conviction and energy, and he will go much farther.

Because of Plekhanov's opposition, Trotsky did not become a full member of the board. But participated in its meetings in an advisory capacity, which earned him Plekhanov's enmity.

In late 1902, Trotsky met Natalia Sedova (1882–1962), who soon became his companion. They married in 1903, and she was with him until his death. They had two children together, Lev Sedov (1906–1938) and Sergei Sedov (1908–1937), both of whom would predecease their parents. Regarding his sons' surnames, Trotsky later explained that after the 1917 revolution:

In order not to oblige my sons to change their name, I, for "citizenship" requirements, took on the name of my wife.

Trotsky never used the name "Sedov" either privately or publicly. Natalia Sedova sometimes signed her name "Sedova-Trotskaya".