who or what is the god of small things?

It would be worth your while to re-read Chapter 11 of this incredible novel, entitled "The God of Small Things." One of the key aspects of Roy's style that is employed throughout the book is the way that she uses repetition to highlight important aspects of what she is trying to convey. Therefore we as readers are presented with phrases that echo throughout the narrative as we bounce back and forward between the present and the past. One of these phrases is given to us in Chapter 11, which describes the ecstatic union of Ammu and Velutha:

Who was he, the one-armed man? Who could he have been? The God of Loss? The God of Small Things? The God of Goose Bumps and Sudden Smiles? Of Sourmetal Smells - like steel bus-rails and the smell of the bus conductor's hands from holding them?

It is clear then that the title "The God of Small Things" comes to be applied to Velutha in the tale, however at the same time, symbolically it comes to mean much more. At the very end of the tale, note how Roy talks about what Velutha and Ammu focus on in their relationship:

Even later, on the thirteen nights that followed this one, instinctively they stuck to the Small Things. The Big Things ever lurked inside. They knew that there was nowhere for them to go. They had nothing. No future. So they stuck to the small things.

Thus the God of Small Things could be said to be the God of those who possess a determination to extract what joy and pleasure they can out of life no matter how hopeless the situation and how temporary that pleasure may be. Velutha and Ammu, in their union, transgress "The Love Laws" as Roy calls them, and thus they recognise that what they can savour is only in the now and is at best temporary. And yet they make the most of it, in spite of the crushing end that they know is just around the corner. In the face of such "Big Things" as caste, race and inequality, perhaps it is only the "Small Things" that can be lived for.