Uraziel is a greater spirit that inhabits the Ring of Solomon, and the most powerful one known. It is the only one known to hold the power to actually act as a gate to the Other Place. Uraziel was sealed by an unknown, ancient civilization into the ring in which he resides.
Uraziel's ring had the ability to summon countless spirits of every class including Marids with relative ease and nearly instantaneously without the hassle of the summoning process, and even to dismiss those summoned by other magicians. King Solomon used the ring to summon vast armies of spirits to obliterate his enemies and carve out a massive empire. There is also no immediate danger to the ring-wearer since all the summoned spirits are bound to Uraziel's will. However, Uraziel's power is so great that anyone who touches the ring experiences great pain, amplified more so when it is put on. Use of the ring sucks the life force out of the user at various rates that seem to be proportional to the difficulty/magical expenditures of the spirit within. Continuous use of the ring leads to premature aging and eventually, death. Most spirits lack the constitution to use the ring, its aura being so powerful that it literally melts the essense of Bartimaeus when he touches it directly. Actual use of the ring by a summoned spirit (as seen when Bartimaeus used the ring to summon Uraziel) causes a tearing effect that in time would destroy the spirit. This occurs becase the spirit is naturally drawn into the gate to the Other Place the ring produces, while at the same time it is anchored by their summons, thus the power of the Ring is confined to powerful human magicians.
Uraziel's other abilities include spontaneous matter transfer and the casting of all types of spells including those technically available only to magicians.
The limit of Uraziel's power, if it exists at all, is unknown, but it is clear that he is able to dispose of marids casually and without any struggle. When Bartimaeus offers to attempt to destroy the ring, Uraziel replies "The Ring cannot yet be broken", possibly implying that it might well be broken at an unspecified future date.