Collet Barker (1784-30 April 1831), military officer and explorer, explored areas of South Australia. Little is known of his early life. He joined the British Army in 1806, becoming a captain in 1825. In 1829 he was commander of the settlement at King George's Sound in Western Australia. In 1831, on the recommendation of Charles Sturt, who had discovered the mouth of the Murray River the previous year, Barker was sent to explore the coast of South Australia around St Vincent's Gulf to see if another channel from the Murray entered the sea there. In April 1831 Barker and his party arrived at Cape Jervis on the Isabella. He examined the coast and found that there was no channel. He then explored the ranges inland, north of the present site of Adelaide, and climbed Mount Lofty. He then went overland to explore the area around Lake Alexandrina and Encounter Bay. On 30 April the mouth of the Murray was reached. Barker swam across the narrow channel, went over a sandhill, and was never seen again. A few days later the party learned that Barker had been killed by the local Aboriginal people.

The town of Mt Barker in South Australia is named after him, as is the Australian Electoral Division, the Division of Barker in south-eastern South Australia.