This Strategy-Note article was written by a anonymous person and was published first on "Lord of the Rings Online (lotrtcg.decipher.com)".
When Gandalf arrived with Saruman and the other Wizards in Middle Earth, more than two thousand years before the events described in The Lord of the Rings occur, Círdan the Shipwright saw in him a hidden strength. Even though Saruman was the head of their order, Círdan saw that Gandalf was the greatest of the Wizards and entrusted him with Narya, the Red Ring of Fire. When Saruman betrayed Middle Earth to Sauron, Gandalf was indeed shown to be wiser and more powerful. It the end, it would be Gandalf who would lead the final fight against Sauron and aid in the destruction of the One Ring.
Despite exercising little overt power during The Lord of the Rings, there seems to be little that Gandalf cannot do. He defeats the Balrog - a beast from which all the orcs in Moria fled - in single combat, he comes back from the dead, even long-lived elves turn to him for wisdom, and he gets along with all the races of Middle Earth. He's the uniting force in the alliance of the Free Peoples.
The Gandalf culture works in a similar way - Gandalf does almost everything in the card game that other cultures can do. While other cultures have obvious strengths and weaknesses, the Gandalf culture is more subtle, yet versatile and well rounded. This makes the Gandalf culture a great "support" culture. Almost any deck can benefit by having Gandalf in it to fill in the gaps in the deck. Gandalf has stealth-like cards, card drawing abilities, condition removal, and powerful skirmish cards. With him, you can complement Dwarves, Elves, Men, or a combination of different races to create a winning deck.
Gandalf himself is one of the stronger companions in the game. Each of the versions of Gandalf has certain strengths. Gandalf, Greyhame allows you to bring back important companions like Aragorn, Ranger of the North that you may have discarded early. Most players will tell you that having that Aragorn fully healed for the final push into site nine is almost a guaranteed win. Another Gandalf that can play a great supporting role is Gandalf, The Grey Pilgrim. Since he draws cards at the start of your turn, he is not limited by the "Rule of Four" and as many veteran card players will attest, drawing more cards is never a bad thing. When Gandalf, The White Wizard is armed with his staff and his sword, he can take on most minions in the game. Even as a one companion culture, he is a force to be reckoned with!
Strength of Spirit is a great example of an all-purpose Gandalf card. Many Free Peoples cards require you to exert to get some effect, from Legolas, Greenleaf to Filibert Bolger's skirmish canceling ability. With Gandalf and Strength of Spirit, almost any deck can benefit by being able to exert without actually placing wounds for the effort. This kind of cross-culture utility is what Gandalf excels at. For example, the Gondor culture is great at winning skirmishes, but they have no way to remove conditions from the Shadow player's support area - this leaves them vulnerable to many Shadow strategies. By slapping in Gandalf and a Sleep Caradhras or Grown Suddenly Tall, that deck can overcome this deficiency.