Jupiter

Guru is the great benefic. It signifies wisdom, teachers, children, law and religious life, and its method is expansion — whatever it touches gets larger.

That is not unconditionally good, and reading it as such is the most common beginner error. Jupiter in a difficult house expands the difficulty. Jupiter on a malefic amplifies it.

Its aspects matter more than most: Jupiter alone aspects the 5th and 9th from itself in addition to the 7th, which means a well-placed Jupiter reaches three houses rather than one.