Post an anime character that is already strong or genius from the very beginning

Kakashi Hatake

L (Death Note) was already strong and genius from the beginning of the series

Akatsuki Ousawa from Aesthetica of a Rogue Hero is both

Eishiro Sugata is already strong AND a genius both at the same time from Heaven's Lost Property

Lelouch - Code Geass (genius)

Yamraiha, possibly before the beginning.

Accelerator X3

~he was powerful enough to get an army after him when he was a kid

Killua Zoldyck from Hunter x Hunter; a trained assassin from birth. Despite having 2 older brothers, his family seems to think Killia has the most potential & was made the family heir.

That's why he is the supportive sidekick & the series focuses on weak brain-dead Gon instead. They balance eachother out & keep eachother from doing stupid things. He's also an excellent battle strategist.

Killua is always 30 steps ahead of poor Gon.

This series also has a neutral character called Hisoka who's powers seem to know no limits. He's so sure of himself, that he lives everyday life on the edge, hoping he'll meet somebody who's strong enough to kill him.

Niizuma Eiji from Bakuman

Ami from Sailor Moon.

Kisuke Urahara (Bleach)

Itachi Uchiha has pretty much always been strong. He's intelligent, too, so he fits the question to a T.

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Hanamiya Makoto from Kuroko no Basuke was a genius from the beginning of probably even before middle school. ( He has an IQ of over 160 ) Don't mind about the picture. ( it is still him though )