Translation guide
The English word "former" has two main uses: referring to something that existed or happened in the past (previous), and referring to the first of two things mentioned (the former vs. the latter). Japanese expresses these meanings differently.
Describing someone who previously held a position, role, or status, or something that existed before.
former president · former girlfriend · former job · former glory
Prefix meaning 'former' or 'ex-'. Used for people and roles. Very common and neutral.
former president
former girlfriend
Prefix meaning 'previous' or 'former'. Often used for official positions or titles, especially in formal contexts.
former prime minister
Prefix meaning 'old' or 'former'. Used for things, systems, names, etc., not usually for people.
former system
the former Soviet Union
Phrase meaning 'former' or 'once'. Emphasizes that something existed in the past but no longer does. Can be used for people, places, or things.
former lover
former glory
Referring to the first of two previously mentioned items (the former vs. the latter).
Literally 'the former one'. Used in formal or written contexts when contrasting two things. Often paired with 後者 (こうしゃ, the latter).
The former is better.
In casual speech, Japanese often avoids 'the former' by simply repeating the noun or using context. Using 前者 can sound stiff in conversation.
There is a dog and a cat. I like the former (the dog) better.
元 (もと) is the most general for 'former' people/roles. 前 (ぜん) is common for official positions and implies the immediate predecessor. 旧 (きゅう) is used for things/systems/names, not people. For example, 元大統領 (former president in general), 前大統領 (the immediately preceding president), 旧ソ連 (the former Soviet Union).
前者 (ぜんしゃ) is only for abstract items in a list, not for people. To say 'my former boss', use 元上司 (もとじょうし) or 前の上司 (まえのじょうし), not 前者の上司.
Compare the former and the latter.