Congrats to @Sunspeck for guessing the last cat! It was Greywing! Here's the next one..

Fur of black,
Also white,
Rolling hills,
Always in sight,
Underground & above,
Forever in question,
Until the day,
His heart is broken,
Travels far,
To get revenge,
On the cat,
That made the end,
Meets with the cat,
That tags along,
Finding the answers,
He should have known all along,
To sad to kill,
He left to go home,
Best friend follows,
But stays where he belongs,
Became leader,
Of the great clan,
Led long great life,
Until the end,
Took the journey,
And finished it too,
Ending not in sorrow,
For he knew,
That the cat he had chosen,
Would renew.

Who am I?

Sorry it's so long!!
And that I took so long to do it!!