Olver has "an insolent grin he had picked up somewhere."
Mat:

seen from Australia
seen from China
seen from United States
seen from Hong Kong SAR China
seen from Hong Kong SAR China
seen from Hong Kong SAR China
seen from India
seen from Japan

seen from United States
seen from United States

seen from France
seen from Malaysia
seen from United States

seen from United States

seen from Hong Kong SAR China

seen from United States

seen from Hong Kong SAR China
seen from India
seen from Hong Kong SAR China

seen from Malaysia
Olver has "an insolent grin he had picked up somewhere."
Mat:

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For Aviendha’s part, Olver seemed to make her uneasy, which Mat did not understand at all.
At a guess, it's because she sees him as a potential threat that she cannot neutralize because killing a child would be dishonorable.
Mat constantly describing Olver as ugly gets 100 times funnier when you headcanon that Olver looks like Mat did as a kid.
(WoT Book 6 Spoilers) Mat is included in this count.

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Casting call for Olver like "seeking desperately ugly child to play tiddy- and boardgame-obsessed orphan"
By de-aging Mat’s sisters, giving him a shitty home life, and giving him fear/guilt about possibly killing the little girl who offered him her Birgitte doll, the show is absolutely setting up both Mat adopting Olver and Mat falling for royally-fucked-up Tuon and I am HERE for it.
However, I am rooting for girl!Olver because the image of like a tiny 10-year old girl hero-worshipping this sweaty disaster general and nurturing a one-woman revenge quest against the Aiel who murdered her parents is extremely funny, and also I want to see Tuon taking a professional interest in Mat’s tiny child and like, really taking the stones games with her seriously as a training tactic.
this is pretty much what happened