Who is Tommy Laurence from Trainspotting and what is their importance?

Tommy Laurence is a good friend of Renton and Begbie and a part of the core group of the novel. At the beginning of the narrative, he is not a heroin user. He drinks, does a speed, and dates a girl called Lizzy. One day, he forgets her birthday and goes to an Iggy Pop concert instead. She dumps him, and in anguish, Tommy asks Renton to help him try heroin. Renton obliges, and Tommy begins a steep decline into addiction.