|The cub will be influenced by this.|
When I create my story characters, I start with the parents. I go even more in the past if necessary, but the parents are a must, whether they actually appear in the story or not. If asked how to make the story character seem real, I'd suggest: "Start with the parents."
We all are who and what we are partly due to our parents. I'm not saying we're just like them; in many cases, we're not. People can become this or that in spite of their parents, not just because of them -- but one way or another, their parents will have some influence on them.
What if they're orphans? What if their grandparents or relatives brought them up? What if they were taken away from their parents because they were criminals? What if they grew up in a foster home, or an orphanage, or on the streets? The lack of the parental presence influences people just as much as the presence does -- the person won't be the same if they grew up with a loving mother and a loving father and if they grew up on the streets, looking up at their gang leader. It's also not the same if a human brought them up, or a pack of wolves, or if it was an alien family or an elven or a dwarf family.
I usually start at the moment the characters' parents first met. How did they meet? How old were they at the time, what were they doing, what were their hopes and dreams? How did they marry (if there was a marriage)? How did the pregnancy go, was it risky, was it difficult? Did the parents even want that child? What kind of childhood did that character have? What sort of relationship did they have with the parents? And so on, until I have the character's entire life story in my mind, starting at the moment their parents met.
I don't write all these things down. I often write none of them down, and most of them never even show up in the story, at least not directly -- but the result is there. And the result is a character you know almost everything about, starting from the time before they were even born -- and the readers will sense that, they will find your characters believable and will care about them. On top of that, you'll find the writing easier, because the picture of the character is so clear in your head (it could also mean the character won't always do what is convenient for the writer to do -- but hey, it's quite possible to adapt to that), and the whole thing doesn't take too much effort, just some daydreaming about the characters who refuse to leave your head anyway, so you might as well play with them.