If a person has a criminal past, will a judge or jury hear about it during trial?

An accused person’s character is usually inadmissible (not allowed) at trial. Character evidence, however, becomes admissible if the defendant or his attorney introduces it into evidence. There is this rule of criminal procedure because the law doesn’t want something from a one’s past to influence their decision about the current case. There are, however, exceptions to character evidence admissibility.