As of my knowledge cutoff in September 2021, the most expensive artwork ever sold is Leonardo da Vinci's painting "Salvator Mundi". It was sold at auction in November 2017 for $450.3 million, making it the most expensive artwork ever sold at the time.
The painting depicts Jesus Christ in a Renaissance dress, holding a crystal orb in his left hand and raising his right hand in a gesture of blessing.
The painting is believed to have been painted by da Vinci around the year 1500, and it is one of only about 20 known works by the artist. The painting's buyer has not been publicly identified.