The first one the comes to mine is from the first FR book I read, Darkwalker on the Moonshaes. It was Gavin the smith of Cantrev Myrrdale. He captured my attention right away at his introduction.
He was encountered unexpectedly and mistaken at first for a Firbolg, because of his giant size. He was instantly warm and generous to Prince Tristan and his companions but soon became a tragic character widowed and the father of two dead daughters at the hands of Laric and his Bloodriders.
He was so large he wielded a giant hammer of with a shaft six feet in length and head that could not have weighed less than 50 pounds, impossible to think such a weapon could be wielded, but he did so with feathery ease.
He quickly became a hero of the Ffolk at the battle of Freeman's Down and the died tragically at the battle of Caer Corwell. He alone was able to stand physically and block the charge of Laric and his immensely powerful undead Bloodriders taking several with him as he saved Robyn's life in a courageous last stand.
I don't remember many of the ancillary characters from FR novels, but the one that immediately comes to mind is the Spriggan in RA Salvatore's Hero. For those who don't know, Spriggans are gnome/dwarf-like creatures who can transform themselves into giants. The way RA Salvatore depicts them, they are very strange and malevolent creatures. The scenes involving them were some of my favorite parts of the book.