An intruder in a dream usually reflects boundaries that feel violated -- a sense that your space, privacy, or safety has been compromised somewhere in waking life. The vulnerability in these dreams is often the real message, more than the intruder's identity. If you're able to face or remove the intruder, the dream may be showing you a boundary you're finally ready to defend.
The Moon is in conflict with those who are ruled by Mars, and Mars is in conflict with those ruled by the Moon. - Picatrix (Andalusia, ~1000.AD)