Henri Charles Loeillot or Loeillot-Hartwig, usually known as Karl Loeillot, was a French painter and lithographer.

Loeillot was born in Stettin, Germany, and died in Paris, France.

The signature of Loeillot-Hartwig, K or Karl Loeillot is found on lithographs, which often depict studies of horses, made by other artists, such as Horace Vernet. His name is also found on a series of 16 lithographs under the general title: Recueil de sujets Grecs (Collection of Greeks topics), which Loeillot created in 1824 on behalf of Choisy faience factory. These illustrations were inspired by the Greek Revolution of 1821 and used to decorate faience objects, such as crockery and mainly dishware sets.

These lithographs were used predominately by Choisy factory for the decoration of 12-piece dishware sets, whereas the factories in Montereau and Toulouse selected only some of them and completed the rest of their sets using themes inspired by the work of other artists, such as Hippolyte Bellangé and Henri Decaisne. The variety of these sets is great, since the frames of the dishes were decorated with different variation of ornaments each time.

Loeillot's illustrations were also used to decorate vases, tea sets, stamped fabrics and wooden cases.