Lucas - as played by Felix Mallard- was/is real. He was a good friend of the Lockes' father when he was killed. As a teen, he was possessed by a piece of Whispering Iron and was taken over by a demon. The demon's base form was Lucas' original body (again as played by Mallard). He used the Idenity Key to transform into a woman - played by Laysla De Oliveira - and was killed. This form is generally referred to as "Dodge" in the show, including in the credits.
Later, the Echo Key is used to bring her back to life. Since she was in the Dodge(/De Oliveira) from when she died, her echo was also in the Dodge(/De Oliveira) form when she came back. Without access to the Identity Key, she was stuck in the Dodge(/De Oliveira) - and trapped in the wellhouse - for a long time.
When she escapes the wellhouse and regains the identity key, she creates the "Gabe" face (as played by Griffin Gluck) to manipulate Kinsey. She also tries to use the Dodge(/De Oliveira) from to try and manipulate Tyler. She doesn't spend much time in the original Felix(/Mallard) form. Out-of-universe, this is largely because Malliard wasn't available for much filming but in-universe, there are pictures of Lucas(/Malliard) around and people who knew him (most notably Ellie) so he could be caught if using that form especially in the Lockes' orbit.
So the Dodge(/De Oliveira) and Gabe(/Gluck) forms were created by the key, while the Lucas(/Malliard) form was "real" and couldn't be duplicated by the key, despite the fact that we spend much more time with Gluck then any of the others and we also spend more time with De Oliveira then Mallard.
