Which Maurya defeated Alexander?

No Maurya Defeated Alexander. When Alexander was coming and returning Chandragupta was still in training stage.

The most deadly battle with Alexander was fought by king puru or porus whose result is still debated. But one thing is certain that it hammered the Macedonian courage like hell.

Chandragupta began conquest after Alexander had already left and then dethroned Magadha ruler Dhanananda and then conquered most of the other janapadas and Formed Akhand Bharat.

He defeated Selucus Nicator in 305 BC who was one of the close confident and satrap of Alexander.