He had a heart of gold.

an absolute heart of gold.

Right up to the end he remained active.

He had a tremendous amount of energy and that transferred to everybody around him. Not only was he a good leader, he was a good teacher.

For her heart was cold to all but gold,And the rich came not to woo --But honored well are charms to sellIf priests the selling do.

His bark is worse than his bite. He's got a gruff exterior but underneath is a heart of gold.