The Hell Bitch

Here's what I have to say about her:

The Hell Bitch is a fine mare that has been Newt Call's horse for several years. She is the only character besides Newt Call that has spanned both the miniseries and the two seasons of the syndicated television show. Though spirited, the Hell Bitch has served Newt Call faithfully. (She was less faithful in the STREETS OF LAREDO, however, where she kicked Newt to death. This ultimately lead to Woodrow Call's career as a bounty hunter, but that is a different story.)

History:

She is Woodrow Call's favorite horse.
Woodrow Call gave Newt his horse, but not his name, before he left to take Gus' body back to Lonesome Dove, Texas.
After Woodrow finally admitted to Newt's parentage, Newt took the Hell Bitch to Curtis Wells.
The riderless Hell Bitch bravely arrives in CW, clueing the townspeople of Newt's untimely "death."
The Hell Bitch is stabled in the CW livery, the part-time home of Newt Call, and is presumably shoed by Unbob.