One of the most notable was the concept of Alan Kay, The Dynabook concept. But the first ever true laptop or portable computer available commercially was the Osborne 1 in 1981 that is under the CP/M operating system. Although it is a bit too far from what we call laptop today and it cannot be used using batteries, it created a high impact as it was the first portable computer that professionals can take with them. Its a size of a portable sewing machine and allowed to be carried on aircrafts.
There are also some claims that the Xerox Note Taker was the first portable computer however, only 10 prototype were released that made it unofficial.