Blockstream's own leadership page describes Adam Back as "Co-founder and CEO of Blockstream" and states that he "invented Hashcash, the proof-of-work algorithm cited by Satoshi Nakamoto in the Bitcoin whitepaper, as the future basis for its mining function".
Hashcash was published in 1997 as an anti-spam measure: make the sender burn a small, verifiable amount of computation before a message is accepted. Bitcoin reuses the same mechanism for a different purpose, which is to make the cost of rewriting history real rather than notional.
The same page records that before Blockstream he held senior roles at technology companies including Microsoft, EMC, VMware and Zero-Knowledge Systems, and that he holds a computer science PhD in distributed systems from the University of Exeter. Blockstream's company history names him among the founders in 2014, alongside Erik Svenson, Pieter Wuille and others.