HYDRA, especially under Strucker’s direction, was a ruthless and efficient organization that took a number of heroes down to the wire - and yet for Strucker this is not good enough.

Source: https://screenrant.com/doctor-doom-baron-von-strucker-enemies-hydra/

Smith’s gripes were overheard by an undercover Hydra agent (as SHIELD had been fully infiltrated by Hydra spies at this point in the MCU’s history), and that agent introduced Smith to Baron Strucker, Hydra’s lead scientific mind and current commander.

Source: https://screenrant.com/most-important-mcu-character-agent-mark-smith/