is the 加名词还是形容词

都可以

Sb. is the＋形容词最高级＋名词 that I have ever seen (known/heard/had) 某人是我见过的（知道的／听过的／遇见）最……的人

如:

She is the loveliest girl that I have ever seen.她是我见过的最可爱的女孩。

John is the cleverest student that I have ever known.汤姆是我知道是最聪明的学生。

She is the most interesting person that I have ever heard.她是我听过的最有趣的人。

He is the most generous man that I have ever met.他是我遇见过的最慷慨的人

the是特指某物的冠词，放在句首

如：The ball is behind me.有的时候在一些国名全称之前，如：the U.S.A.