Heko (ἥκω) means 'I have come' or 'I am present' — it is a perfect-tense-like verb that emphasizes the present state of having arrived. It appears about 27 times in the New Testament. It differs from erchomai (to come/go) in emphasizing the state of arrival rather than the motion of coming.
Jesus uses heko in powerful declarations of His mission: 'I have come [heko] to do your will, O God' (Hebrews 10:9, quoting Psalm 40:7–8). In John 8:42, Jesus says: 'I have come [heko] from God.' Revelation 3:3 warns: 'if you do not wake up, I will come [heko] like a thief.' The eschatological uses are particularly striking — Revelation 18:8 declares that Babylon's plagues 'have come [heko] in a single day.' The arrival of Christ — first in incarnation, finally in judgment — is the pivot of all history. Every use of heko in the NT points toward the one great Coming that defines everything before and after.