Step 1: Understanding the Concept: 
The question asks to identify the leader and main ideologue of the short-lived but influential artists' collective, Group 1890. 
Step 2: Detailed Explanation: 
Group 1890 was formed in 1962 in Bhavnagar, Gujarat. The group, comprising twelve artists, sought to create an art that was modern and authentically Indian, independent of both the Bengal School's revivalism and the Western academic styles. The name "Group 1890" came from the house number of J. Pandya, where the group's manifesto was written. The artist, writer, and activist J. Swaminathan was the group's founder, leader, and chief spokesperson. He wrote their manifesto and was the driving intellectual force behind their vision of a "living, struggling Indian art." While Jeram Patel was a prominent member, Swaminathan was the undisputed leader. K.C.S. Paniker was associated with the Cholamandal Artists' Village in Madras and was not part of this group. 
Step 3: Final Answer: 
Group 1890 was formed under the leadership of J. Swaminathan.
Rearrange the following parts to form a meaningful and grammatically correct sentence: 
P. a healthy diet and regular exercise 
Q. are important habits 
R. that help maintain good physical and mental health 
S. especially in today's busy world