The correct answer is B. Menander.
Menander was an Indo-Greek king who ruled over the northwestern part of the Indian subcontinent in the 2nd century BCE. He was a great conqueror and a wise ruler, and he is best known for his dialogues with the Buddhist monk Nagasena, which are recorded in the Buddhist work Milinda Panho.
Demetrius was another Indo-Greek king who ruled over the same region in the 2nd century BCE. He was also a great conqueror, but he is not as well-known as Menander.
Eukratises was an Indo-Greek king who ruled over the same region in the 1st century BCE. He was not as successful a conqueror as Demetrius or Menander, and he is not as well-known.
Heliocles was an Indo-Greek king who ruled over the same region in the 1st century BCE. He was also not as successful a conqueror as Demetrius or Menander, and he is not as well-known.
Menander was the most famous Indo-Greek ruler because he was a great conqueror, a wise ruler, and a devout Buddhist. He is best known for his dialogues with the Buddhist monk Nagasena, which are recorded in the Buddhist work Milinda Panho. These dialogues are a valuable source of information about Buddhism and Indo-Greek culture.