Recognize that there are two steps to analyzing the admissibility of character evidence: (1) whether the evidence is admissible in the first place; and (2) whether the manner of presentation is proper.
As to the first step, evidence of a character trait to prove action in conformity with the trait (i.e., to prove that someone acted a certain way in the case at hand because they acted the same way in the past) is inadmissible in civil cases. In criminal cases, it is admissible under limited circumstances, as set forth below.
As to the second step, assuming character evidence is admissible in the first place, it can be proven by proof of the person’s reputation for the character trait, or by a witness’s opinion about the trait. Opinion testimony must be either a proper lay or expert opinion. It cannot be proven by proof of specific acts establishing the character trait unless the trait is an essential element of the charge, claim, or defense.