aggressor

Compared meaning: someone who attacks (noun).

比较义项：攻击者、发起攻击的一方（名词）。

• attacker

  The most general term for someone (or something) that attacks, used for fights, sports, or even computer systems; carries little emotional or legal weight.

  最通用的说法，指发起攻击的人（或事物），可用于打斗、体育比赛甚至计算机系统等场景；感情色彩和法律色彩都不强。

  The virus was designed to make the attacker's identity hard to trace.

  这种病毒的设计目的就是让攻击者的身份难以追查。

• assailant

  A more formal word, common in legal or news contexts, for someone who physically attacks a person; it always refers to a person, never an object or a country.

  较为正式的词，常见于法律或新闻语境，专指对某人实施人身攻击的人；只能指人，不能指物品或国家。

  The victim could not identify her assailant in the police lineup.

  受害者在警方的指认环节中无法认出袭击她的人。

• aggressor 本词

  Emphasizes who started the fight or conflict first and is often used to assign blame; it can describe a person, but is especially common for a country in a war or dispute.

  强调是谁率先挑起冲突，常用于追究责任；既可指人，也常用来指在战争或争端中率先发难的国家。

  Diplomats agreed that the larger nation was clearly the aggressor in this dispute.

  外交官们一致认为，在这场争端中，那个较大的国家显然扮演了侵略者的角色。

All three mean someone who attacks. Attacker is the most general, covering fights or hacking. Assailant is formal, used in law or news for someone who attacks a person. Aggressor blames whoever started a conflict, for a person or country. Its sports sense isn't compared.

这三个词都表示“攻击者”，但语义侧重不同：attacker最通用，可指人、物甚至抽象的攻击行为（如体育比赛中的进攻方、网络攻击者），语气中性；assailant专指对人实施人身攻击的人，多见于新闻报道或法律语境，语气较正式；aggressor强调“率先挑起冲突”的一方，常用来描述挑起争端的人或发动战争的国家，带有道德评判色彩。这里不比较attacker在体育比赛中表示“前锋、进攻球员”的用法。