One of the major themes in Shantaram is friendship. The relationship that grows between Lin and his newfound Indian best buddy, Prabaker or Prabu Kharre, is an epic friendship. Prabu is almost like a cartoon character of all things India, with his gigantic smile and unwavering loyalty; his loss represents a major tragedy for Lin.
Prabaker is not only Lin's best friend; he's also his guide to India. As the only native character in the novel with any sort of dimension, he represents the entire native population up against the colorful cast of foreigners. It's a big job, but Prabu never backs down from a challenge.
Prabaker is known for his 1000-watt smile, which makes him seem more like a caricature than a believable character. Lin's first vision of him is among a crowd of tour guides, all hustling for clients at the bus stop:
He shouted for silence from his companions, and then turned to me with the widest and most radiant smile I'd ever seen.
"Good mornings, great sirs!" he greeted us. "Welcome in Bombay! You are wanting it cheap and excellent hotels, isn't it?" (1.1.60-61)
Between his gigantic smile (a feature which is repeatedly referenced in the novel) and his endearing way of speaking, with its extra plurals ("Good mornings"), misplaced prepositions ("Welcome in"), and bonus direct objects ("You are wanting it cheap and excellent hotels"), Prabaker comes off as a harmless, comic character.
Whereas most of the other characters in Shantaram come from outside of India, Prabaker is Lin's closest local friend. He's also Lin's ticket to the "real" Bombay, showing him not only the best tourist sights and restaurants, but also the dark side of the city.
Prabaker, then, is sort of like a gatekeeper to his country. This is especially true when he invites Lin to visit his home village in Maharashtra state, an honor that Lin accepts. When Didier finds out about the invitation, he says that Lin's "little friend is beginning to love [him]" (1.4.25). That love, the foundation of Lin's and Prabu's friendship, is revealed when Prabu shows India to Lin.
While almost all of the gangsters and, of course, Lin survive all sorts of crazy adventures, Prabaker isn't so lucky. He dies in an awful car crash, just like the one that he and Lin experienced during the dark tour of Bombay. To make matters worse, it's in the taxi that Lin bought him as a wedding gift.
In the hospital, Lin sees the damage: "Tubes and metal pipes were taped to his face—what was left of his face. That great smile, that gorgeous, solar smile, had been ripped from his face. It was simply… gone" (4.29.173). The smile, Prabaker's shining glory, is violently taken away from his friends and family, along with their happiness—sad.