Detailed Explanation:

Raj Kumar Shukla, a poor peasant from Champaran, invited Mahatma Gandhi to Bihar in 1917 to address the grievances of indigo farmers suffering under the exploitative tinkathia system imposed by British planters.

Shukla persistently followed Gandhi from the 1916 Lucknow Congress session until he agreed to visit Champaran, marking Gandhi's first major Satyagraha in India. Rajendra Prasad and others joined later as supporters, but the invitation came solely from Shukla.

Therefore, Raj Kumar Shukla invited Gandhi to Champaran, making Option 1 the correct answer.