The curator of the Lahore Museum goes by two titles: first, the narrator refers to him by his official profession, which is curator of the Lahore Museum. A curator is someone who manages a museum's collection and decides what goes up on the walls and where.
The Lahore Museum is a truly amazing real-life building that still stands in Lahore to this day. It was constructed in the 1860s for the British Indian government's Punjab Exhibition of 1864, marking the transition towards Britain's more direct colonial administration of India in the late nineteenth century. And—fun historical fact—John Lockwood Kipling, Rudyard Kipling's father, was the curator of the Lahore Museum when Kipling was a child. So we might assume that the kindly, knowledgeable curator in Kim is modeled after Kipling's own father.
But while the narrator may call the curator, well, curator, the lama has a whole different title for this minor character: the Keeper of the Images at the Wonder House. The lama also likes to call him the Fountain of Wisdom (1.55), and he continues to mention him periodically throughout the novel even though the curator only appears in person in the first chapter of Kim.
Why is this guy so particularly important to the lama? Well, from the lama's nicknames for him, we are guessing that it is because the curator symbolizes pure knowledge to the lama. His wisdom and education in Indian religious art, even though he is not himself a Buddhist, inspires a deep respect in the lama. And because the curator gives the lama a new pair of glasses to take with him on his religious pilgrimage, the lama credits the curator with giving him a head start on his search for the River of the Arrow.