One of the original cards to appear in the Alpha version of the first collectible card game Magic: The Gathering. Serra Angel is probably the best known white creature in the game... which says quite a bit considering Wizards of the Coast has printed somewhere close to 700 different white creatures as of the writing of this node.

Here's a Quick Breakdown of the Card:

3WW
Creature - Angel
Flying.
Attacking does not cause Serra Angel to tap.
4/4

What makes this card so special?:

When Magic: The Gathering was first concieved, many of the creatures were sub-par in comparison to the instants and sorceries that could destroy them. In retrospect, this was a good thing. If a creature was too powerful, it could be Terrorized, slapped aside the head with a Lightning Bolt or simply Counterspelled before it even resolved. As the game progressed, though, many of the original creatures were set aside and improved upon so that the Sorceries and Instants were on par with the permanents.

Amongst this rabble of bad creatures, a few stood out. Serra Angel was an uncommon (which meant, in the early stages of the game's development, that people had her, or had seen her, but neither too frequently) that could supply, simultaneously, the role of both a good attacker, and a solid defender in a world full of medium-powered vanilla creatures. Its respectable casting cost and evasion also meant that it could race ridiculously over-costed powerhouses in the early stages of the game's development and finish the job of killing the opponent while he was embroiled with getting ready to strike. It also seemed to participate deliciously well with the white sorcery Wrath of God, which cleared the board of all creatures. It commonly required so many creatures to swarm/take down the Serra Angel, that your opponent would over-commit; dropping three or four creatures on the board. While you would lose your Serra Angel when you cast Wrath of God, your opponent would commonly lose four other creatures in the trade, netting you card advantage.

Serra Angel was printed in Alpha, Beta, Unlimited, Revised and Fourth Edition of the main game. Up until her departure, she was considered one of the main staples in white... which oddly lead to Wizards decision of not reprinting her in Fifth Edition. At the time, Serra Angel was hogging all of the spotlight for good strong white creatures. In order to experiment with other interesting strong cards, Serra Angel had to be pulled out of the main set so cards like Seraph and Archangel could shine. Oddly, by the time Serra Angel had returned in Seventh Edition (and reprinted again in Eigth Edition), the environment had swung so much that she was just another well-costed potent creature. Her simplicity, though, continues to expose new players to the duality of White: The ability to effectively hurt the opponent while protecting its controller.