Is clozapine a benzodiazepine?

No: Clozapine is considered a 2nd generation antipsychotic medication, typically used in schizophrenia, that antagonizes quite a few neurotransmitter receptors, eg Dopamine d1 & d4 plus serotonin 5ht2 & cholinergic muscarinic ones, too. It's a very effective drug when used under close observation but can only be prescribed under restricted distribution due high risk for agranulocytosis, etc.

Antipsychotic: Not a benzodiazapine. Clozapine (brand names: Versacloz, FazaClo, Clozaril) is an antipsychotic medication used as a treatment for refractory Schizophrenia & for Schizophrenia or Schizoaffective Disorder associated with recurrent suicidal behavior. It has been used off-label for refractory bipolar disorder, intermittent explosive disorder & PTSD.