Scaled Composites Stratolaunch

The Scaled Composites Model 351 Stratolaunch, or "Roc", is a solitary testbed aircraft built by Scaled Composites for Stratolaunch Systems to carry air-launch-to-orbit (ALTO) rockets, and subsequently repurposed to offer air launch hypersonic flight testing after a change of ownership. It was announced in December 2011, rolled out in May 2017, and flew for the first time on April 13, 2019, shortly after the death of founder Paul Allen.

Source: Wikipedia — Scaled Composites Stratolaunch (CC BY-SA 4.0)