第/最后 + Numeral + 任 + Title
The word 任 (rèn) functions as both a measure word for terms of office and a verb meaning "to hold a post." As a measure word, it is used to count successive holders of a position, such as 第一任总统 (first-term president).
他是这所大学的第三任校长。
tā shì zhè suǒ dàxué de dì sān rèn xiàozhǎng.
He is the third president of this university.
她曾任公司副总经理,经验非常丰富。
tā céng rèn gōngsī fù zǒngjīnglǐ, jīngyàn fēicháng fēngfù.
She once served as the deputy general manager of the company and has very rich experience.
新任市长上周正式就职了。
xīn rèn shìzhǎng shàng zhōu zhèngshì jiùzhí le.
The newly appointed mayor officially took office last week.