Then again, I seem to remember Sherlock Holmes and Moriarty showing up on the show as well, but IIRC that wasn't an especially successful effort.
Yes, "Sherlock Holmes in the 23rd Century" was a backdoor pilot for a spinoff in which Holmes fell through a time warp at Reichenbach Falls (ignoring everything from "The Empty House" onward) and arrived in the future, where he teamed up with an alien named Whitson and a tough, gun-loving female descendant named Mycroft Holmes. Moriarty -- played by Jonathan Harris! -- had himself cryogenically frozen and revived in the same era so that he could continue his battles of wits with Holmes.
Coincidentally, a few years later there was an entirely unrelated animated series called Sherlock Holmes in the 22nd Century
, in which Holmes's honey-preserved corpse is revived by future science so that he can battle a clone of Moriarty, and he's teamed up with a robot Watson and a tough female cop named Lestrade.