To

Used to show direction, place, or position, such as going toward something. It also appears before a verb in its basic form, as in 'to eat' or 'to go.'

From Old English 'tō' meaning 'in the direction of, for, with respect to.' It is related to German 'zu' and Dutch 'toe.' Over time, it took on many grammatical roles, including marking the infinitive form of verbs.