Step 1: Recall context.
The Third International, also called the Comintern (Communist International), was founded in 1919 in Moscow to unite communist groups worldwide under one platform.
Step 2: Identify founder.
It was established under the leadership of Vladimir Lenin after the Russian Revolution to spread socialist ideology.
Step 3: Analyze options.
(A) Karl Marx: Incorrect, he founded the First International in 1864.
(B) Lenin: Correct — founder of the Third International in 1919.
(C) Friedrich Engels: Co-founder with Marx, but not of the Third International.
(D) Robert Owen: Associated with cooperative movement, not communism.
Step 4: Conclusion.
Correct answer is (B) Lenin.