Gideon Mantell and Richard Owen, whose rivalry is kept intact.
And Gideon's eventual (from his perspective) wife Mary Ann Woodhouse.
H. G. Wells shows up as the inventor of several time machines.
The Dreamer has many historical figures in it, including Nathan Hale.
Dresden Codak features several historical figures in cameo roles, but a recurring character is Tiny Carl Jung.
Girl Genius has R. van Rijn, aka Rembrandt van Rijn, more commonly known in real life as Rembrandt — in our world, a famous Dutch painter; in the Gaslamp Fantasy world of Girl Genius, a Spark and the creator of the famous Muses of the Storm King, mechanical works that have still not been paralleled 200 years later.
The Storm King himself is the equivalent of Louis XIV, the Sun King. However, the Storm King is Andronicus Valois, whereas Louis was of the House of Bourbon, suggesting that in Girl Genius the House of Valois never died out.
Lovely Lovecraft: H. P. Lovecraft, obviously, as well as his mother.
Mayonaka Densha being a time travel murder mystery involving Jack the Ripper includes not only the man himself but cameos from various other figures involved with the case such as Inspector Abberline, Mary Kelly and various other Ripper victims (Including speculated and unconfirmed ones).
Albert Speer is one of the central characters in Misguided Light.
with bad parenting skills, Sir Francis Drake