Why does the name of ハチ公 【こう】 include Katakana instead of Hiragana?

Question

It seems strange because the name ハチ公 【こう】 combines Katakana and Kanji in one word.

Answer 1

The nickname ハチ公 consists of the name ハチ followed by the suffix 〜公.

Katakana is a common choice for writing names, even if the actual name is written with kanji.

The suffix 〜公 is described in 大辞林 as follows

こう【公】

［一］（名） [...]

［二］（代） [...]

［三］（接尾）
①身分の高い人の名に付けて、敬意を表す。「家康━」
②人や動物の名前に付けて、親しみ、あるいはやや軽んずる気持ちを表す。「忠犬ハチ━」「熊━」

The suffix 〜公 is added to the names of people (of high standing) to show respect or (by extension) to names of people or animals to express affection/intimacy.