Who is Ruby Rose's father? The Wikia says that Taiyang Xiao Long, Yang's father, first married Summer Rose, Ruby's mother. But why isn't Ruby's name Ruby Xiao Long? This might mean that Ruby isn't the real daughter of Taiyang, probably his adopted daughter.
TaiYang Xiao Long is both Yang &amp; Ruby's father.

Yang's mother is unnamed as of Season 2. Ruby's mother is Summer Rose, who is Yang's step-mother.

I have two theories as to why Ruby is Ruby Rose not Ruby Xiao Long.

Theory 1

Summer Rose was insistent that her name be carried on, and so Ruby was given the surname Rose. As Memor-X has said in the comment, a husband taking a wife's surname isn't all that rare nowadays.

Theory 2

It was a convenient choice for the writers - Ruby and Rose are both very vividly red items, whereas Yang Xiao Long can be translated as Small Dragon of the Sunshine or Little Sun-Dragon, reflecting Yang's powerful, fiery personality &amp; battle ability quite well.

Theming the characters with their colour seems to be quite important in RWBY - For instance, check out their pajamas below - Yang has a fiery heart on her tank top, whilst Ruby has rose-patterned bottoms.



I suspect we may find out more if/when Yang's mother's identity is revealed.