True, but states have very significant restrictions on character evidence, particularly "prior bad acts." The theory is that a wrongdoer already paid the penalty for that prior act and should not be punished again, so the jury should not hear such evidence and punish the guy for the prior bad act.
As is true with every rule governing evidence, the exceptions are voluminous. Earlier I wrote about the acronym "MIMIC," generally used to identify the wrongdoer. Think about the movie "Point Break," where the bank robbers wore masks of former Presidents. If those guys are caught and punished and later another person robs a bank wearing the mask of a former President, the prior bad act can be used to prove, "It's the same guy."
Also, prior bad acts can be used if the party which moved to suppress such evidence says something or does something that makes the prior bad act relevant, generally called "opening the door." In the Rittenhouse case, the imbecile prosecutor asked Rosenbaum's roommate if Rosenbaum was "on medication." The defense pounced and turns out the roommate knew a ton about the medication, talked about why he had the medication, what it was meant to treat, the fact he got it that morning after being released from the hospital.
The most common "prior bad act" that is admissible are prior felony convictions that constitute a moral depravity or dishonesty, on the theory that conviction or plea to a felony proves untrustworthiness. That is a prime reason why criminal defendants almost never testify - most have prior felony convictions that are admissible if the defendant testifies.
Lawyers rarely introduce something called direct character evidence, specifically, a witness saying, "This guy is good" or "this guy is honest." The reason for this is that such witness can be asked about his or her knowledge of prior actions by the person about whom the character evidence is offered. "Did you know he was arrested for beating his wife?", "Did you know she was the subject of a child services investigation for failing to feed her kids?"
Yeah, pass. Don't try to offer such evidence.