あいつ, 彼奴, きゃつ, かやつ, あやつ
Pronoun, Usually in kana, Colloquialism, きゃつ and かやつ are masc.
he, she, that guy
あいつが僕のことを「ばかなやつ」っていったんだよ。
は
Particle, pronounced わ in modern Japanese
1. topic marker particle
2. indicates contrast with another option (stated or unstated)
3. adds emphasis