he is gone. = 他已離開了。
he was gone. = 他曾經離開過。(含"已回來"之意,如 he was gone, but now he is back.)
he has gone. = 他(為了某原因)離開了。(含"He has gone (for something/some reasons)"之意,如 he has gone for a walk,他去了散步)
he had gone. = 他曾經(為了某原因)離開了。(同上,只是過去式,亦含"已回來"之意)
圖片參考:http://l.yimg.com/f/i/tw/ugc/rte/smiley_22.gif