  Let $n\in\mathbb{N}$ and let $A$ be a closed linear operator (everywhere
bounded or unbounded). In this paper, we study (among others) equations of the
type $A^*A=A^n$ where $n\geq2$ and see when they yield $A=A^*$ (or a weaker
class of operators). In case $n\geq3$, we have in fact a new class of operators
which could placed right after orthogonal projections and just before normal
operators.
