"Chad was an anomaly. He was calm. Assured. Constantly studying," wrote the director on Sunday morning.
"The ancestors spoke through him," he added. "What an incredible mark he's left for us."
Boseman died on Thursday at home in Los Angeles with his wife, Taylor Simone Ledward, and family by his side.
He had been diagnosed with bowel cancer four years ago, undergoing treatment while filming hit movies like Avengers: Endgame, 21 Bridges and Spike Lee's Da 5 Bloods.