maxByOrNull

Returns the first character yielding the largest value of the given selector function or null if there are no characters.

inline fun <R : Comparable<R>> CharSequence.maxByOrNull(selector: (Char) -> R): Char?(source)

val text = "Kotlin is great"
val maxChar = text.maxByOrNull { it.code }   // character with the highest Unicode code point
println("Character with highest code point: $maxChar")

Source