Which political organization did Kazi Lhendup Dorji Khangsarpa found in Sikkim?

Sikkim Praja Mandal

Answer: Sikkim Praja Mandal
Kazi Lhendup Dorji Khangsarpa founded the Sikkim Praja Mandal in Sikkim.

Kazi Lhendup Dorji Khangsarpa (1904):
A prominent figure in the democracy movement in Sikkim;
He established the Sikkim Praja Mandal and later led the Sikkim State Congress;
In 1962, he founded the Sikkim National Congress;
Following an electoral triumph, he spearheaded the campaign for Sikkim's integration with India;
After the integration, the Sikkim Congress merged with the Indian National Congress.