A set adverbial phrase meaning 'as usual' or 'as always', often used to describe habitual actions or predictable situations.
彼はいつものごとく遅刻した。
He was late as usual.
いつものごとく、彼女は一人でカフェに座っていた。
As always, she was sitting alone in the café.
A fixed phrase combining いつも (always) + の (possessive particle) + ごとく (classical adverbial form of 如し, meaning 'like' or 'as'). The ごとく part is a classical Japanese form that survives in set expressions.