Why did Ong Khan offer Temujin (young Gengis Khan) a position?

Why did Ong Khan offer Temujin a position?

Toghril’s (Ong Khan, died 1203)) acceptance of Temujin (Genghis Khan) as his ‘foster son’ held advantages for both men, and Toghril’s relationship or ‘ceremonial kinship’ with Temujin’s deceased father (they had been andas or blood brothers) made the ‘alliance’ all the more likely. On the latter point, Jack Weatherford, in Genghis Khan and the Making of the Modern World says:

Temujin’s father, Yesugei ..... had once been the anda of Ong Khan, and they had fought together against many enemies. The tie between the men had been stronger than merely patron and vassal because when they were quite young, Yesugei helped Ong Khan become khan of the Kereyid people by overthrowing his uncle, the Gur-khan, or supreme ruler. In addition, they had fought together against the Merkid and were allied at the time of Temujin’s birth, when Yesugei was on the campaign against the Tatars.

Mongol Empire c. 1207 showing the different tribes. Image source.

For Toghril / Ong Khan, there was not just the fact that Temujin (and his two brothers who were also accepted as ‘foster sons’ at the same time) was the son of his anda; he was also a young man with a growing reputation for daring and initiative. Toghril had plenty of enemies, including members of his own family, and saw enough in Temujin to offer him the leadership of a group of young warriors (which Temujin declined).

Accepting Temujin proved to be a smart move for, when Toghril was later deposed by an uncle, Temujin helped him regain his position. Prior to that, Toghril had helped Temujin when his wife Börte had been taken captive.

Why did Temujin seek out Ong Khan?

Weatherford explains steppe culture further and one reason why Temujin sought out Toghril / Ong Khan

According to steppe culture, politics were conducted through the idiom of male kinship. To be allies, men had to belong to the same family, and therefore every alliance between men not connected through biology had to be transformed into ceremonial or fictive kinship. Thus, with Temujin’s father and the would-be Kereyid leader having been ceremonial brothers as andas, Temujin now sought to be treated as a son to the old man.

Temujin, recently married, did this by using his wife Börte’s dowry (which he would normally have given to his father):

Börte thus joined Temüjin’s family, bringing a sable coat as dowry. Temüjin gave the sable coat as a present to the powerful KEREYID khan Toghril (later ONG KHAN),

Source: Christopher P. Atwood, 'Encyclopedia of Mongolia and the Mongol empire' (2004)

In the turbulent world of the rivalries of the Mongol clans, a powerful ally such as Toghril / Ong Khan would prove very useful:

By giving Ong Khan the wedding gift, Temujin was recognizing him as his father; and if Ong Khan accepted, he would be recognizing Temujin as his son and therefore entitled to protection.

Source: Weatherford

Why didn't Temujin seek out Ong Khan earlier?

The reasons for not seeking out Ong Khan earlier were most likely:

1. Temujin was only about 9 when his father died so, as a child, he had nothing to offer Ong Khan in return for his patronage. Further, the mere fact that he was a child would make it very unlikely that he would have been able to.
2. Temujin killed one of his half-brothers, bringing disgrace upon himself for quite some time. It seems unlikely that any potential patron would want to offer protection under such circumstances, and Temujin would have known that.
3. Later, Temujin was a captive slave and may have been in this state for as long as ten years.

In the years following his father Yisugei’s murder, Temujin and his family had endured much hardship. His mother Hoelun (Oelun)

was seen as a paragon of heroic motherhood, raising her sons in great adversity.

Ö’elün was abandoned on the steppe with her five children, Yisügei’s minor wife, Sülchigei, her two sons, and a certain number of retainers.

Source: Atwood

Then, at around the age of 15, Temujin had been involved in the killing of one of his half-brothers. Soon after, he became the captive of a rival clan but eventually managed to escape.

Why didn't Ong Khan, do anything to help Temujin when the latter's father was killed by the Tartars (or Tatars)?

None of the sources offer any explanation for this, but there are a couple of pointers to possible reasons:

1. Ong Khan's realm bordered that of many rulers who were constantly seeking to expand their lands. The Tartars were on Ong Khan's eastern border and, as vassals of the Jurchen, may have been too powerful a force for to meddle with at the time.
2. Ong Khan does not appear to have been a particularly capable warlord. Temujin's family were outcasts so Ong Khan may have been neither inclined nor able to help them. He may also have been too preoccupied dealing with family rivals (he had had several of his brothers killed and was later temporarily deposed by an uncle).
3. According to Atwood, Ong Khan was not an especially admirable character:

Despite the turbulent struggles of his youth, the SECRET HISTORY OF THE MONGOLS portrays the mature Ong Khan as a lax and indecisive ruler, cruel to his brothers, excessively indulgent to his son...

Ong Khan's bond with his anda Yesugei may have been strong at one time, but such bonds did get broken (Temujin's childhood anda later turned against him). Also, we can gleam something of Ong Khan's character from his later actions: he deceived Temujin over a planned wedding and then fought against the adopted son who had sought (and been granted) his protection.

For the record, Temujin defeated Ong Khan at the Battle of Jeje’er Heights in 1203.

Other sources:

Don Nardo, 'Genghis Khan and the Mongol Empire' (2010)

Christopher P. Atwood, 'The Sacrificed Brother in the "Secret History of the Mongols"'. In Mongolian Studies, Vol. 30/31 (2008 and 2009), pp. 189-206.