How did Stalin become dictator of the USSR?

Thanks to his position of General Secretary, Stalin had ultimate control over the party. After Lenin died in 1924, Stalin was in a position to remove all other contenders for leadership. Stalin used bureaucratic shuffles and denunciations to remove minor contenders. He exiled Leon Trotsky, Lenin’s right hand man and obvious successor, by turning public opinion against him by not telling Trotsky about Lenin’s funeral. This made Trotsky look as if he did not care for the most loved man in Russia, whereas Stalin did, because he went to Lenin’s funeral and honoured him. Trotsky, later turned up dead in Mexico, murdered with an ice pick. Was this to do with Stalin? Stalin then turned his attention to two men, Bukharin and Rykov who criticised his process of collectivisation. Bukharin wanted a return to the New Economic Policy, but was unable to rally enough supporters to challenge Stalin. Stalin accused Bukharin of factionalism which had been banned by Lenin since 1921. Other members of the politburo sided with Stalin and Bukharin was removed from the institution in November 1929. Rykov was also removed due to his association with Bukharin. Huge show trials were conducted by supporters of Stalin, at which both Bukharin and Rykov were tried and executed. Stalin made certain he had no opponents.