Mein früherer Chef war streng, aber zuverlässig.

Because früherer is an adjective placed before the noun Chef, so it has to take an adjective ending.

Here, mein früherer Chef is a masculine singular noun phrase in the nominative case. After mein, German uses what learners often call mixed declension. In this pattern, the adjective takes -er in the nominative masculine:

• mein früherer Chef
• dein neuer Lehrer
• sein alter Freund

So früher by itself means earlier or formerly, but before Chef you need the declined form früherer.

It is in the nominative case because it is the subject of the sentence.

The subject is the person or thing doing or being something. In this sentence:

• Mein früherer Chef = subject
• war = verb
• streng, aber zuverlässig = description of the subject

So the phrase has to be nominative, which is why you get mein früherer Chef.

Because mein already works as a determiner, similar to my in English. In German, possessive words such as mein, dein, sein, ihr, and so on usually take the place of an article.

So you say:

• mein Chef = my boss
• not der mein Chef

This is similar to English: you say my boss, not the my boss.

Because they come after the verb sein and are being used as predicate adjectives. Predicate adjectives do not take adjective endings in German.

Compare:

• ein strenger Chef = an adjective before the noun, so it takes an ending
• Der Chef ist streng = an adjective after ist, so no ending

The same applies here:

• war streng
• war zuverlässig

So the rule is:

• before a noun → adjective usually gets an ending
• after sein/werden/bleiben → adjective stays in the basic form

Because German main clauses normally follow the verb-second rule.

In a normal statement, the finite verb goes in the second position:

• Mein früherer Chef = first element
• war = second element

Then the rest follows:

• streng, aber zuverlässig

So the sentence structure is very standard German word order.

War is the simple past form of sein.

• ist = is
• war = was

The sentence uses war because it is talking about someone in the past: my former boss was strict, but reliable.

Also, früherer Chef already suggests that this person is not your current boss, so the past tense fits naturally.

Yes. Both are possible, but there is a small difference in tone.

• mein früherer Chef = my former/previous boss; very common and natural
• mein ehemaliger Chef = my former ex-boss; also correct, but often a bit more formal or official

In everyday conversation, früherer is often very natural.
In formal writing or official contexts, ehemalig is also common.

Be careful with the form, though: it would have to be mein ehemaliger Chef, not mein ehemalige Chef, because the adjective still needs the correct -er ending.

Because aber is a coordinating conjunction, and in German it is normally preceded by a comma when it links two parts of a sentence.

So:

• streng, aber zuverlässig

This comma is standard German punctuation.

In German, Chef means boss, manager, or person in charge.

This is a classic false friend for English speakers, because English chef means a professional cook. In German, a cook is Koch or Köchin, not Chef.

So in this sentence:

• Mein früherer Chef = my former boss

Because Chef is a noun, and all German nouns are capitalized.

That is why you see:

• Mein
• früherer
• Chef
• war
• streng
• aber
• zuverlässig

Only Chef is capitalized because it is the noun.