John Koko, the vocalist and bass player of the Makaha Sons, a group that helped make Hawaiian music popular, died Monday. He was 51.

Koko had battled heart problems since childhood and was moving forward with plans for a heart transplant, said his older brother, Jerome Koko.

The Nanakuli native joined the Makaha Sons of Niihau in 1982. The group, which formed in 1976, has gone through several reorganizations. When John Koko entered the group, he joined brother Jerome, Moon Kauakahi and the world-famous Israel Kamakawiwoole.

When Kamakawiwoole died at age 38 from complications associated with morbid obesity in 1997, the group shortened its name to Makaha Sons.

Career highlights included three performances at New York City’s Carnegie Hall and before President Bill Clinton, Jerome Koko recalled. They released more than 20 albums.

In the last six to eight months Koko started to show signs of fatigue on stage. Because of his deteriorating health, plans were put on hold for upcoming performances in Argentina, Brazil and Germany, Jerome Koko said.

In addition to his brother, John Koko’s survivors include his wife, Tonia; four sons; and two grandchildren.