Kumar was at the top of the rock when a hail storm hit. The other 40 or so people stayed at the top, while he decided to get back down.
Emergency personnel received several 911 calls around 3:40 p.m. reporting a man had fallen off the cables, which span about 400 feet up Half Dome, according to Park Ranger Kari Cobb.
It has been estimated that Kumar fell more than 100 feet, but the exact length hasn't been determined. Dozens of people witnessed him fall, Cobb said.
Half Dome, a granite monolith and one of the most popular hikes in Yosemite, is 17 miles roundtrip. Cobb said the experience of climbing it is "like hiking up a big, granite dome."
Yosemite Park officials advise hikers to wait for sunny weather before hiking Half Dome. It was raining with intermittent hailstorms Saturday.
"The weather was not ideal for the hike," Cobb said. "That definitely played a big part. It gets really slippery when it gets wet."
Cobb said Kumar's body was being recovered late Sunday morning.
The last person to fatally fall from Half Dome was a Japanese hiker in June 2007, who also slipped and fell from the cables.