A lot is known about many of Lenin's allies (and his political rivals too). Also there were quite a few people who switched between being allies and rivals of Lenin during the period, prompted by the political rifts in the party. Lenin's first key ally was Yuri Martov. Martov and him met when they were both young organizers for the RSDLP in Petersburg and had similar ideas on how to transform the party. Lenin in this period wanted to organize a party newspaper which would be the nucleus around which an organization would form. They both formed an alliance in exile and became key party leaders. At first they were united against the older leaders of the party- most notably Plekhanov. But in the London conference of 1903 the editorial board of the paper they created (Iskra) split and this provoked a split in the party into two wings Bolsheviks and Mensheviks. They split because Lenin and Martov had proposed two distinct visions for the party. Lenin wanted it to be a highly disciplined party of "professional revolutionaries" i.e. people who were actively committed to fostering revolution and Martov wanted a more decentralised party in which sympathisers could join. In time the split created two parties.

In this period Lenin gained a reputation for being fairly rigid and the Bolsheviks were attacked by Mensheviks for being too centralising. A lot of very able party leaders went over to the Mensheviks while others were critical of him within the Bolshevik party. But he attracted a number of key followers who stayed with him for a long time. His closest ally, and effectively his deputy in the Bolshevik party was Grigory Zinoviev. He was not a brilliant theorist like Lenin or Martov but he was an exceptional public speaker, a good popularizer and very loyal to Lenin. Not many people liked him on a personal level, he was seen as arrogant but without much to back it up. Two Bolsheviks who were critics of Lenin and often rivals with him are very worth mentioning because they are personally interesting. Alexander Bogdanov was his main rival for leader within the Bolshevik party and an animosity developed between them. He was a doctor and scientist who also wrote a science fiction novel called Red Star and would attract a significant following before being sidelined by Lenin. He later died after the revolution when performing blood transfusion experiments on himself in an effort to investigate rejuvenation. A very important Bolshevik leader who was a good personal friend of Lenin's but often at odds with him was Nikolai Bukharin. Bukharin was much younger than Lenin and was at times close to Bogdanov and developed into a leading figure of the left wing of the party. He was close to Lenin in exile though and exerted a substantial theoretical influence on him- his book on imperialism was the inspiration for Lenin's most famous work Imperialism: The Highest Stage of Capitalism. In his political testament Lenin labelled Bukharin the favourite of the party and there is no doubt he was personally popular. He would become a major leader in the revolution but was outmaneuvered by Stalin and eventually killed in the 30s.

Two women were extremely important political allies to Lenin and central to his personal life. His wife Krupskaya was with him from 1898 until his death in 1924. She worked with him constantly, edited his books, helped with the management of the part (she was according to Trotsky at the centre of all organizational work) and was a very important political leader in her own right. During the revolution she played a major role in the development of the Soviet education system. Inessa Armand was a French-Russian socialist Lenin met in exile who became his closest friend and confident and with whom he had an affair. She was a central leader of the party in exile and co-ordinated the Bolsheviks in Europe and Russia. After the revolution she was briefly a very powerful figure, head of the women's section in the party and editor of the women's newspaper, but died of the Spanish flu in 1920.

WW1 and the revolution caused political alliances to shift dramatically. Because both Trotsky and Lenin opposed the war and later the Russian Provisional Government they were able to build an alliance. Trotsky was one of the most brilliant Russian socialist leaders and had initially formed a close bond with Lenin before spliting with him after the 1903 London conference. In 1917 they were reunited and shared a close friendship and important political alliance until Lenin's death. Other Mensheviks or independent minded Bolsheviks like Lunacharsky also returned to Lenin's circle in this period. One person he never redeveloped an alliance with, however, was Martov- and this remained a point of great sadness to both of them. Martov remained a Menshevik and, although he agreed with Bolshevik policies in 1917 resolutely condemned their methods leading to his and Lenin's total estrangement. He was eventually forced into exile when the Mensheviks were criminalised. The revolution also caused considerable strain in Lenin's relationship with his old deputy Zinoviev. Zinoviev and Kamevev disagreed with the October revolution and openly criticised it. Though they were later reconcilled to Lenin, Zinoviev never regained his old position as Lenin's most trusted ally which was a great cause of resentment to him and prompted his jealousy of Trotsky which would ultimately lead him to form an alliance with Stalin with disastrous consequences.

That's most of Lenin's key allies, hope it helps!