Matt Hawkins is a marine diver.
Well, yes but when we first meet him, he is the designer of undersea robots which require his knowledge of how things work deep underwater but he does a lot of his work on dry land.
Several years prior to starting this interesting profession, Hawkins was a Navy SEAL for several years and a darn good one. Then a mission to Afghanistan went terribly wrong and some of the men under his command were killed and Hawkins was nearly one of them. Besides coming close to dying he saw one of his legs terribly mangled. When he pressed hard to find out what went wrong and why and who, the Navy fought back and gave him a psychiatric discharge and tried to forget about him.
That was then and now he makes devices that work beneath the waves. At least he did until a super hush-hush government agency with no name comes asking for his help.