Top 十 is the cross radical and the entry's indexing radical. Historically it is the schematic top of a soldier's helmet sitting on the body below; the whole char originally pictured an armoured warrior shouldering a heavy load.
Lower 兄 carries the human-figure portion: a person 儿 with a 口 mouth above. In 克 it stands in for the body that supports the helmet, evoking the soldier who can subdue or overcome an enemy - hence the meanings overcome, gram, subdue.
