To take charge of an item of business, or an obligation, as a personal initiative
He took it upon himself to check the reports.
If you take something on or upon yourself, you decide to do it without asking anyone for permission or approval. "Knox had taken it on himself to choose the wine...", "He took upon himself the responsibility for protecting her...", "The President absolved his officers and took the blame upon himself."
If you take something on or upon yourself, you decide to do it without asking anyone for permission or approval