This is the 8157th most frequent Japanese word.
尽く
"尽く" means "to exhaust, devote, or do something to the utmost."
Here, '尽くして' comes from the verb '尽くす', which means 'to exhaust' or 'do one's utmost.' It is used to describe the act of putting one's full effort and energy into something.
彼は力を尽くして仕事に取り組んでいる。
He is working on his job with utmost effort.
As illustrated, '尽くした' signifies the completion of action to the fullest extent or best of one's ability in achieving something or pursuing one’s goal.
運命に尽くすべき最善を尽くした。
He did his best to fulfill his destiny.
In this sentence, '尽くしている' also originates from '尽くす' and implies the ongoing dedication or devotion of one's resources, such as time or efforts, to a cause.