"No job is big or small. Some may think what they do is insignificant, but I have found my destiny. It is to make wigs," says Mr Kumar.
"It's my very small contribution towards giving people, who are facing a grave illness, some hope and dignity," he adds.
Born in a farming family, Mr Kumar ran away from home at a young age to work with a film crew which assisted studios making Kannada-language films.
Working long hours as an apprentice, he learnt the craft of making natural hair wigs - a painstaking job where every strand is hand woven.
This is the 10th article in a BBC series Unsung Indians, profiling people who are working to improve the lives of others.
More from the series:
The doctor who delivers girls for free
Cancer survivor bringing joy to destitute children
A messiah for India's abandoned sick
The woman whose daughter's death led her to save others
The man saving Mumbai water one tap at a time
The man who chases fires
Nurturing slum children's passion for cricket
The woman who electrified a village and took on a mafia
Helping villagers ask uncomfortable questions
He didn't know anything about cancer or chemotherapy - and the hair loss that accompanies it - until he met a customer who was heartbroken after losing her hair because of the illness.
"My life changed from the moment when I saw the look on her face after I'd fitted the wig on her," he says.
From making wigs for television and movie stars, Mr Kumar switched to only making wigs for cancer patients.
He buys natural hair from the Hindu temple town of Tirupati - where it is considered auspicious for pilgrims to have their heads shaved.
He is helped in his work by his wife, Lalitha Marishetty, who cleans the hair by boiling it with detergents and drying it out in the sun. She then makes little bundles of five strands each by knotting them together.
The couple work out of a tiny hole-in-the-wall shop and together, they have made more than 20,000 wigs for people with cancer.
Mr Kumar keeps his prices low as most of his customers are poor - a wig from his shop costs between 7,000 rupees ($105; Â£73) and 25,000 rupees ($377; Â£263), depending on the length of hair used.
"It doesn't pay much," he says, "but the satisfaction I get from this job is immense."
Marishetty Kumar, a wig-maker based in the southern Indian city of Bangalore, is helping cancer patients to live a life of dignity, writes the BBC's Shilpa Kannan.