If you want to summon a familiar to your side during battles and such, or just to help out, you have a lot of options. Owls, bats, mice, snakes, and more. But if you want to upgrade to a dire wolf, it depends. The dire wolf is not listed as a familiar in the official rules, but there’s nothing that says a player can’t have a celestial dire wolf if the DM allows it. Rangers can also have a dire wolf as an animal companion, but the main problem there is that a dire wolf is much more intelligent than a regular wolf. If your ranger decides to use the dire wolf’s intelligence for something, they will have a much greater advantage than if they use a regular wolf. Again, it might not be a game breaker if both the player and the DM are aware of this and the player doesn’t take too much of an advantage with the intelligence boost. Still, it is not in the official rules. Finally, druids might wonder if they can shift into a dire wolf through wild shape. The answer is that they can, and they can do so from levels 1-5 thanks to the low CR of the dire wolf. So unless your DM is willing to do a bit of homebrewing, that’s the only way you can have a dire wolf as an ally.