The Greek noun despotēs refers to an absolute master — one with unrestricted authority and ownership over others. In the Greco-Roman world it described the master of slaves (as in 1 Timothy 6:1–2; Titus 2:9; 1 Peter 2:18). It was also used of God and Christ as the absolute sovereign Lord over all creation (Luke 2:29; Revelation 6:10).
When Simeon uses despotēs in Luke 2:29 ('Sovereign Lord, now dismiss your servant in peace'), he is attributing to God the highest possible authority. The martyrs in Revelation 6:10 cry to God as despotēs — the absolute Sovereign — asking how long before he judges and avenges their blood. The title affirms that God's authority is not limited, conditional, or delegated — it is inherent and absolute. This is both a comfort (nothing is beyond his control) and a call to accountability: as servants of the absolute Master, disciples are fully answerable to him.