incompetent
adjective
°Unskilled, lacking normally expected degree of ability.
"Having an incompetent lawyer may be grounds for a retrial, but the lawyer in question probably doesn't know that."
°Unable to make rational decisions, insane or otherwise cognitively impaired.
"The charged was judged incompetent to stand trial, at least until his medication started working."
noun
°A person who is incompetent.