The adjective clause has a "subject and a verb" with a relative pronoun
Explanation:
He, who is intelligent, is praised by all.
Here, ‘who is intelligent’ is an adjective clause.
The word that describes the noun is called as an adjective. For example, He is an intelligent student, and hence, praised by all. Here, intelligent is an adjective.
To change it into an adjective clause, you will just have to introduce relative pronouns such as why, what, who, which and that.