Expert
Noun
たつじん
一つのことに全てをかけないと、真の達人にはなれないぞ。
If you won't put all your eggs in one basket, you won't be a real master.
ビエトは、カメラの達人です。
Viet is a master of the camera.
父は、ピザ配達の分野で、世界レベルの達人であると評判になっています。
My dad is famous for being a world-level master in the realm of pizza delivery.
A person who has "attained" is someone who knows much. He/She is a master or expert, obviously.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.