Several parts combine into one character.

Phonetic-semantic compound: 亻 (person) + 固 (firm / individual unit, providing phonetic value). The encoded meaning: "an individual unit / one by one". Three forms: 繁體 個 / 新字体 個 / 简体 个 — Mainland China simplified to a radical reduction stripping the entire left side, leaving just the bottom of 固.

Mandarin's most important measure word. 个 (gè) is the universal Mandarin classifier — when in doubt about which measure word to use for any noun, 个 works for nearly everything. This is a foundational fact every Mandarin learner must internalize on day one. It pairs with numbers and demonstratives: — 一个人 (yīgè rén, one person) — 这个 (zhège, this one — neutral final tone) — 那个 (nàge, that one) — 几个 (jǐge, how many) — 哪个 (nǎge, which one) Mandarin uses very specific measure words for many noun categories (条 for long things, 张 for flat things, 只 for animals, etc.), but 个 is the fallback that always works.

Japanese: on-reading コ (ko) — 一個 (ikko, one item — note geminate "kk"), 二個 (niko, two items), 個人 (kojin, individual person), 個性 (kosei, individuality / character), 個別 (kobetsu, individual / separate), 個数 (kosū, number of items). Japanese counting uses 個 for small round-ish objects (apples, balls, eggs); other counters apply for other shapes (枚 for flat, 本 for cylindrical, 匹 for animals, 人 for people). The Japanese counter system is famously complex — 個 covers the "default round object" category.

Note that 個人 (kojin/gèrén/個人) — "individual / private person" — is a foundational modern social-science vocabulary across CJK languages.

Memory aid: a person + something firm = an individual countable unit.