In a lot of RPGs (role-playing games), certain characters (Rangers and Druids from D&D, Hunters from WoW, etc...) can tame an "animal companion" that follows them loyally and does their bidding, helping in combat and sometimes in other capacities as well.
Would something like this actually be possible in real life? Are there any examples of it happening? (I know we've domesticated dogs and used them for a variety of things, including warfare, but I don't think I've ever heard of - for example - a lone adventurer trudging through the wilderness with a combat-oriented canine trotting along at his side).
If so, what animals would best be suited for this?
To clarify, my story takes place in a fantasy world, but magic is uncommon and creatures generally follow the same rules as the real world.
EDIT: It has been noted that this question isn't really worldbuilding, which is fair. I initially thought of it as worldbuilding because it was for a story (as well as, admittedly, some curiosity) and I care about a level of detail and realism. I wanted to find out how realistic this concept of an animal companion was in general, along with some capabilities, limitations, and potential examples. This would be helpful to have in mind when writing, so I could have an idea of what elements would be fantasy (if any).
As it stands the responses and comments have been useful, if not exactly what I was looking for, and for what it's worth I consider my question answered.