Chandragupta Maurya founded the empire — option 4.

What he did. About 321 BCE, with the guidance of Chanakya — also called Kautilya or Vishnugupta — he overthrew Dhana Nanda, the last Nanda ruler of Magadha, and made himself master of Pataliputra. He then drove the Greek garrisons out of the north-west, and in about 305 BCE defeated Seleucus Nicator, Alexander’s successor in the east. By the treaty that followed he gained Aria, Arachosia, Gedrosia and the Paropamisadae — roughly eastern Afghanistan and Baluchistan — in return for 500 war elephants, and Seleucus sent Megasthenes as ambassador to his court.

Notice that the four options are the founder, his son, his grandson and the last ruler — the question is testing the order of the dynasty as much as the name.

The sources for his reign. Megasthenes’s Indica, surviving only in quotations by later Greek writers, describes Pataliputra and the administration; Kautilya’s Arthashastra sets out the theory of statecraft; the Jaina tradition holds that Chandragupta abdicated, became a Jaina monk under Bhadrabahu, and ended his life by sallekhana at Shravanabelagola in Karnataka; and Vishakhadatta’s play Mudrarakshasa dramatises his rise.

The extent of the empire. Under Ashoka it reached from Afghanistan to Bengal and from the Himalaya to Karnataka — the largest empire India had yet seen, and the first to unify most of the subcontinent under one administration.

Hence, the answer is Chandragupta Maurya.