My personal favourite Black Butler characters. DISCLAIMER: opinions are strictly my own. I do not speak for all black butler or anime fans. Yes, i know Ciel himself is not on this list. Sorry not sorry.
#5 Mey-Rin although i (and most other people) thought she was going to be a rather insignificant and irrelavent character, she turned out to have quite the backstory and an irreplaceable charm that cant quite be described.
#4 Alois Trancy Although he is probably one of the most harsh and violent characters, i personally always found him eerily intriguing.
#3 The Undertaker Although he is probably one of the most volatile and mildly creepy characters, i always thought he added a lot of critical elements to the plot.
#2 Grell Sutcliff A classic comic relief character with an intricate backstory that most comic relief characters never get.
#1 Sebastian Michaelis This one is pretty obvious. Who DOESN'T love sebastian honestly?