His intimidating presence was rivaled only by that of his ferocious-looking dog.

rivaled 是动词 rival 的过去分词形式。rival 的意思是"与...匹敌、比得上"，指两者在某个方面具有相当的实力或影响力。这里用过去分词形式表示被动含义，说明"他的气势"被"他的狗"所匹敌。