High entropy random data creating functions?

Are there functions which produce "infinite" amounts of high entropy data? Moreover, do functions exist which produce the same random data (sequentially) time after time?

(I kind of know that they exist -> do they have a specific name?)

Example: Using the function to generate 100 bits of random data. (Great!) *while maintaining high values of entropy. Using the same function to generate 10000 bits of random data. (The first 100 bits generated are the same as the 100 bits of random data generated before) *while maintaining high values of entropy

Further -> how would I go about building these functions myself?