In 1997, Apple acquired NeXT Computer for a deal commonly reported at about $429 million.
Apple announced its intention to buy NeXT in December 1996 and finalized the acquisition in February 1997. Apple was searching for a modern operating-system foundation to replace the aging classic Mac OS, and NeXTSTEP offered a Unix-based technology platform suited to that goal.
The acquisition also brought Steve Jobs back to Apple as an adviser. NeXTSTEP evolved into the technology foundation for Rhapsody and ultimately Mac OS X, making the purchase far more consequential than the price alone suggests.
Sources sometimes report the transaction as $427 million rather than $429 million because of differences in how cash, stock, options, debt, and assumed liabilities are counted. That accounting variation does not change the canonical answer: Apple.