The Taelons are an advanced species in many ways, and are energy-based beings rather than having a material, biological form. They are without gender (but are usually referred to as if they were male, for convenience) and wear a somewhat human-like "skin" effect when dealing with Earthlings: normally they have a translucent appearance.
Roddenberry has created in Earth: Final Conflict an intriguing and complex story of almost magic technology (like cyber-viral implants for human brains and the ability to grow buildings!), mystery, lies, secrets and deception that is absolutely gripping. Apart from re-runs of Babylon 5, it is possibly the most compelling Science Fiction TV series on British television at the moment. Four seasons have now been shown in the UK, on the Sky One Sky/Cable channel, and the series started right from the beginning on the British Sci-Fi Channel in late summer 2001.
There is a comprehensive Web site for the series, and this has links to other related sites.