Jenž, jejž

The relative pronouns jenž, and variations, are a Czech specialty. No cognates appear in other Slavic languges, not even in Slovak. Even many native Czechs don't get these pronouns right when declining them. One of their insteresting features is that inanimate masculine nominative and animate masculine accusative are not identical. In other cases (nouns and adjectives), but not personal pronouns, in all Slavic languages, these two cases look the same. Czech: Mám nový dům. Nový dům je velký. Slovak: Mám nový dom. Nový dom je veľký. Polish: Mam nowy dom. Nowy dom jest duży/wielki. All of them mean I have a new house. The new house is big, where new house is accusative in the first sentence and nominative in the second one.

This doesn't hold true for jenž, though. Jenž can only be masculine nominative, animate or inanimate: Hoch, jenž je tady, je můj syn. Dům, jenž tam stojí, patří mému otci. (The boy who is here is my son. The house that stands there belongs to my father.) If you want the accusative, you use jejž for inanimates and jehož (which also means whose) or jejž for animates: Hoch, jejž/jehož vidím, je můj syn. Dům, jejž vidím, patří mému otci.

It should be said, though, that these pronouns are most commonly used in writing (and even there occasionally erroneously). The spoken language prefers který (and variations), declined as regular adjectives, with cognates in most Slavic tongues.