不需要大寫。
He was a miserable old devil.
他真是個令人厭煩的老傢伙。
He's a crafty old devil.
他是個奸詐狡猾的傢伙。
The leader seemed the devil incarnate.
那個首領好像是魔鬼的化身。
I miss the old devil， now that he's gone.
老傢伙這一走，我還真想他。
She has convinced herself that she is possessed by the devil.
她確信自己被魔鬼附了身。
