Complex sentence: He appears as a main character in the 100th episode "Slice of Life", where his personality is similar to that of the Tenth Doctor, and he is shown to be an scientist and wears the Fourth Doctor's iconic scarf.
Split into simpler sentences: He appears as a main character in the 100th episode "Slice of Life", where his personality is similar to that of the Tenth Doctor. He is also shown to be a scientist and wears the Fourth Doctor's iconic scarf.