JANSZ or JANSSEN, WILLEM (c. 1570-after 1629), first authenticated discoverer of Australia,

was born possibly about 1570, probably at Amsterdam, Holland. Nothing is known of his early life, and he is first heard of in 1598 as a mate on the Hollandia, one of the vessels in the second Dutch fleet to voyage to the East Indies. He returned to Holland, and on 21 December 1599, having been promoted to the position of first mate, sailed again for the Indies. He made other voyages, but when he left Holland in December 1603 in command of the Duyfken, as part of a large fleet, the understanding was that this vessel was to remain in the east for three years, and endeavour to find new sources of trade. On 18 November 1605 Jansz left Bantam for Banda. From Banda an east-south-east course was taken to the Kei group, thence to Aru and the coast of New Guinea at De Jong's Point. Turning south the Gulf of Carpentaria was entered and the Australian coast was discovered at the mouth of the Pennefather River, on the Cape York peninsula, probably in March 1606. The course continued to latitude 13.59 when the Duyfken began her return journey. A visit was made to Prince of Wales Island, the New Guinea coast was again approached, and then a turn was made and Banda was reached in May 1606. For the first time some 200 miles of the Australian coastline had been charted, though Jansz was not aware it was not part of New Guinea.

Subsequently Jansz was in command of various vessels. He returned to Holland in 1611 when he was described in a letter from the chamber of Zeeland as "a very competent and sober man, who has pleased us greatly by his account of trade in the East". About the end of December 1611 he sailed again to the Indies in command of the Orangie. He became governor of Solor in 1614, and in 1617 made another visit to Holland. In January 1618 he went to Java as super-cargo on the Mauritius and arrived at Bantam on 22 August.

In October 1619 Jansz was sent with six ships against the British, surprised four ships which had been loading cargo on the west coast of Sumatra, and captured them. Peace with the British was made soon after and Jansz, who had been made an admiral, was engaged in a joint operation with them against the Philippines. For three and a half years from October 1623 Jansz was governor of Banda. He returned to Batavia in June 1627 and soon afterwards, as admiral of a fleet of eight vessels, went on a diplomatic mission to India. In December 1628 he sailed for Holland and on 16 July 1629 reported on the state of the Indies at The Hague. He was probably now about 60 years of age and willing to retire from his strenuous and successful life in the service of his country. Nothing is known of his last days.