Who introduced merino sheep to Australia and when?

The Father of Australia's sheep industry is often regarded as John Macarthur. He was a man with a great deal of influence in colonial Australia, and it was he who arranged for the first Merino sheep to be brought to Australia from Spain. The first Spanish Merino sheep were brought to Australia in 1796. This type of Merino was a tough sheep which could handle Australia's extreme conditions. There had been little initial success with grain growing - a situation that was rectified as the colony grew - but sheep were an excellent mainstay, easy to maintain and profitable for both domestic and overseas markets.

The first sheep came with the First Fleet in 1788, but these were not merinos.

See the related link about the role of John Macarthur in the establishment of the Merino sheep in Australia.