Books that are bibles for quant funds.

I have been doing some quant analysis/financial engineering in my limited amount of free time, I am wondering if there is a book that you would recommend. I plan on using this knowledge on my personal portfolio. 

I have been reading https://link.springer.com/book/10.1007/978-1-4419…

And I am looking to expand upon my understanding of these topics.

Please leave your recommendations below and provide a 1-2 sentence description as to why that book is of importance.